Revealing Lithium Nitrate-Mediated Solid-Electrolyte Interphase of Lithium Metal Anode via Cryogenic Transmission Electron Microscopy

The cycle stability of lithium metal anode (LMA) largely depends on solid-electrolyte interphase (SEI). Electrolyte engineering is a common strategy to adjust SEI properties, yet understanding its impact is challenging due to limited knowledge on ultrafine SEI structures. Herein, using cryogenic transmission electron microscopy, we reveal the atomic-level SEI structure of LMA in ether-based electrolytes, focusing on the role of LiNO3 additives in SEI modulation at different temperature (25 and 50 °C). Poor cycle stability of LMA in the baseline electrolyte without LiNO3 additives stems from the Li2CO3-rich mosaic-type SEI. Increased LiNO3 content and elevated operating temperature enhance cyclic performance by forming bilayer or multilayer SEI structures via preferential LiNO3 decomposition, but may thicken the SEI, leading to reduced initial Coulombic efficiency and increased overpotential. The optimal SEI features a multilayer structure with Li2O-rich inner layer and closely packed grains in the outer layer, minimizing electrolyte decomposition or corrosion.

Gradient three-dimensional current collector with lithiophilic nanolayer regulation for efficient lithium metal anode construction

Metallic lithium (Li) is highly desirable for Li battery anodes due to its unique advantages. However, the growth of Li dendrites poses challenges for commercialization. To address this issue, researchers have proposed various three-dimensional (3D) current collectors. In this study, the selective modification of a 3D Cu foam scaffold with lithiophilic elements was explored to induce controlled Li deposition. The Cu foam was selectively modified with Ag and Sn to create uniform Cu foam (U-Cu) and gradient lithiophilic Cu foam (G-Cu) structures. Density Functional Theory (DFT) calculations revealed that Ag exhibited a stronger binding energy with Li compared to Sn, indicating superior Li induction capabilities. Electrochemical testing demonstrated that the half cell with the G-Cu@Ag electrode exhibited excellent cycling stability, maintaining 550 cycles with an average Coulombic efficiency (CE) of 97.35%. This performance surpassed that of both Cu foam and G-Cu@Sn. The gradient modification of the current collectors improved the utilization of the 3D scaffold and prevented Li accumulation at the top of the scaffold. Overall, the selective modification of the 3D Cu foam scaffold with lithiophilic elements, particularly Ag, offers promising prospects for mitigating Li dendrite growth and enhancing the performance of Li batteries.

Bipolar Polymeric Protective Layer for Dendrite-Free and Corrosion-Resistant Lithium Metal Anode in Ethylene Carbonate Electrolyte

The unstable interface between Li metal and ethylene carbonate (EC)-based electrolytes triggers continuous side reactions and uncontrolled dendrite growth, significantly impacting the lifespan of Li metal batteries (LMBs). Herein, a bipolar polymeric protective layer (BPPL) is developed using cyanoethyl (-CH2CH2C≡N) and hydroxyl (-OH) polar groups, aiming to prevent EC-induced corrosion and facilitating rapid, uniform Li+ ion transport. Hydrogen-bonding interactions between -OH and EC facilitates the Li+ desolvation process and effectively traps free EC molecules, thereby eliminating parasitic reactions. Meanwhile, the -CH2CH2C≡N group anchors TFSI- anions through ion-dipole interactions, enhancing Li+ transport and eliminating concentration polarization, ultimately suppressing the growth of Li dendrite. This BPPL enabling Li|Li cell stable cycling over 750 cycles at 10 mA cm-2 for 2 mAh cm-2. The Li|LiNi0.8Mn0.1Co0.1O2 and Li|LiFePO4 full cells display superior electrochemical performance. The BPPL provides a practical strategy to enhanced stability and performance in LMBs application.

Difunctional Ag nanoparticles with high lithiophilic and conductive decorate on core-shell SiO2 nanospheres for dendrite-free lithium metal anodes

Lithium metal is an attractive and promising anode material due to its high energy density and low working potential. However, the uncontrolled growth of lithium dendrites during repeated plating and stripping processes hinders the practical application of lithium metal batteries, leading to low Coulombic efficiency, poor lifespan, and safety concerns. In this study, we synthesized highly lithiophilic and conductive Ag nanoparticles decorated on SiO2 nanospheres to construct an optimized lithium host for promoting uniform Li deposition. The Ag nanoparticles not only act as lithiophilic sites but also provide high electrical conductivity to the Ag@SiO2@Ag anode. Additionally, the SiO2 layer serves as a lithiophilic nucleation agent, ensuring homogeneous lithium deposition and suppressing the growth of lithium dendrites. Theoretical calculations further confirm that the combination of Ag nanoparticles and SiO2 effectively enhances the adsorption ability of Ag@SiO2@Ag with Li+ ions compared to pure Ag and SiO2 materials. As a result, the Ag@SiO2@Ag coating, with its balanced lithiophilicity and conductivity, demonstrates excellent electrochemical performance, including high Coulombic efficiency, low polarization voltage, and long cycle life. In a full lithium metal cell with LiFePO4 cathode, the Ag@SiO2@Ag anode exhibits a high capacity of 133.1 and 121.4 mAh/g after 200 cycles at rates of 0.5 and 1C, respectively. These results highlight the synergistic coupling of lithiophilicity and conductivity in the Ag@SiO2@Ag coating, providing valuable insights into the field of lithiophilic chemistry and its potential for achieving high-performance batteries in the next generation.

Design advanced lithium metal anode materials in high energy density lithium batteries

Nowadays, the ongoing electrical vehicles and energy storage devices give a great demand of high-energy-density lithium battery. The commercial graphite anode has been reached the limit of the theoretical capacity. Herein, we introduce lithium metal anode to demonstrate the promising anode which can replace graphite. Lithium metal has a high theoretical capacity and the lowest electrochemical potential. Hence, using lithium metal as the anode material of lithium batteries can reach the limit of energy and power density of lithium batteries. However, lithium metal has huge flaw such as unstable SEI layer, volume change and dendrites formation. Therefore, we give a review of the lithium metal anode on its issues and introduce the existing research to overcome these. Besides, we give the perspective that the engineering problems also restrict the commercial use of lithium metal. This review provides the reasonable method to enhance the lithium metal performance and give the development direction for the subsequent research.

Lithium metal deposition under the geometrical confinement effect: Dendritic copper foam current collector

Dendrite-free lithium is the ultimate goal in achieving the commercial application of lithium metal anode. In this paper, Dendritic Copper Foam Current Collector (DCFC) is prepared by an electrometallurgy method to realize the homogeneous deposition of lithium metal. The deposition behavior of Cu and Li on different interfaces was studied. Firstly, the Cu dendrites constructed on the surface of Cu foam are induced and formed by the potential oscillation generated by the hydrogen evolution reaction. Secondly, the heterogeneous nucleation model reveals that the reason for the dendrite-free lithium deposition on the dendritic copper foam is the geometrical confinement effect. Compared with commercial copper foam, DCFC with hierarchical structure significantly reduces the nucleation energy and deposition overpotential of lithium metal. The in situ optical microscope observation and finite element simulation results confirm our ideas. Electrochemically, DCFC works stably after 1200 h at a lower potential of 36 mV in a DCFC@Li symmetric battery, which is much superior to 75 mV for just 340 h in Cu foam. The ideal collector with a dendritic structure has broad prospects for the practical application of lithium metal anode.

Engineering and regulating the interfacial stability between Li1.3Al0.3Ti1.7(PO4)3-based solid electrolytes and lithium metal anodes for solid-state lithium batteries

InCl3@Li1.3Al0.3Ti1.7(PO4)3-F (InCl3@LATP-F) solid electrolyte powders are designed and fabricated by coating a uniform InCl3 layer on the surface of F--doped Li1.3Al0.3Ti1.7(PO4)3 (LATP-F) solid powders via a feasible wet-chemical technique. The assembled Li/InCl3@LATP-F/Li cell can undergo longer cycles of 2500 h at 0.4 mA cm-2 without obvious increases in the overvoltage compared to 1837 h for the Li/LATP-F/Li cell, and the interfacial resistance demonstrates a sharp decrease from 3428 to 436 Ω for the Li/InCl3@LATP-F/Li cell during the first 500 h. Importantly, the assembled LiCoO2/InCl3@LATP-F/Li cell delivers a high discharge specific capacity of 126.4 mAh g-1 with a 95.42% capacity retention ratio after 100 cycles at 0.5 C, and the value easily returns to 112.9 mAh g-1 when the current density is abruptly set back to 0.1 C after different rate cycles. These improved results can be mainly attributed to the fact that the InCl3 layer with a lithiophilic nature can react with lithium metal to form a Li-In alloy, which can guarantee homogeneous lithium ion flux to avoid the accumulation of ions/electrons across the interface and suppress the growth of lithium dendrites. Moreover, the InCl3 layer can prevent direct contact of the LATP-F solid electrolyte and lithium metal to effectively alleviate the reduction reaction of Ti4+ and preserve the structural stability of the composite electrolyte. Therefore, this work may provide an effective strategy to engineer and regulate the interfacial stability between LATP solid electrolytes and lithium metal anodes for LATP-type solid-state lithium batteries.

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

The practical application of Li metal anodes (LMAs) is limited by uncontrolled dendrite growth and side reactions. Herein, we propose a new friction-induced strategy to produce high-performance thin Li anode (Li@CFO). By virtue of the in situ friction reaction between fluoropolymer grease and Li strips during rolling, a robust organic/inorganic hybrid interlayer (lithiophilic LiF/LiC6 framework hybridized -CF2-O-CF2- chains) was formed atop Li metal. The derived interface contributes to reversible Li plating/stripping behaviors by mitigating side reactions and decreasing the solvation degree at the interface. The Li@CFO||Li@CFO symmetrical cell exhibits a remarkable lifespan for 5,600 h (1.0 mA cm-2 and 1.0 mAh cm-2) and 1,350 cycles even at a harsh condition (18.0 mA cm-2 and 3.0 mAh cm-2). When paired with high-loading LiFePO4 cathodes, the full cell lasts over 450 cycles at 1C with a high-capacity retention of 99.9%. This work provides a new friction-induced strategy for producing high-performance thin LMAs.

An artificial interfacial layer with biomimetic ionic channels towards highly stable Li metal anodes

Lithium (Li) metal with low electrochemical potential and high theoretical capacity is a promising anode material for next-generation batteries. However, the low reversibility and safety problems caused by the notorious dendrite growth significantly impede the development of high-energy-density lithium metal batteries (LMBs). Here, to enable a dendrite-free and highly reversible Li metal anode (LMA), we develop a cytomembrane-inspired artificial layer (CAL) with biomimetic ionic channels using a scalable spread coating method. The negatively charged CAL with uniform intraparticle and interparticle ionic channels facilitates the Li-ion transport and redistributes the Li-ion flux, contributing to stable and homogeneous Li stripping and plating. Furthermore, a robust underneath transition layer with abundant lithiophilic inorganic components is in-situ formed through the transformation of CAL during cycling, which promotes Li-ion diffusion and suppresses the continuous side reactions with the electrolyte. Additionally, the resulting cytomembrane-inspired artificial Janus layer (CAJL) displays an ultrahigh Young's modulus (≥10.7 GPa) to inhibit the dendrite growth. Consequently, the CAJL-protected LMA (Li@CAJL) is stably cycled with a high areal capacity of 10 mAh cm^-2 at a high current density of 10 mA cm^-2. More importantly, the effective CAJL modification realizes the stable operation of a practical 429.2 Wh kg^-1 lithium-sulfur (Li-S) pouch cell using a low electrolyte/sulfur (E/S) ratio of 3 μL mg^-1. The facile yet effective protection strategy of LMAs can promote the practical application of LMBs.

N, F-enriched inorganic/organic composite interphases to stabilize lithium metal anodes for long-life anode-free cells

The practical application of lithium metal batteries is considered to be one of the most promising successors for lithium-ion batteries due to their ability to meet the high-energy storage demands of modern society. However, their application is still hindered by the unstable solid electrolyte interphase (SEI) and uncontrollable dendrite growth. In this study, we propose a robust composite SEI (C-SEI) that consists of a fluorine doped boron nitride (F-BN) inner layer and an organic polyvinyl alcohol (PVA) outer layer. Both theoretical calculations and experimental results demonstrate that the F-BN inner layer induces the formation of favourable components (LiF and Li₃N) at the interface, promoting rapid ionic transport and inhibiting electrolyte decomposition. The PVA outer layer acts as a flexible buffer in the C-SEI, ensuring the structural integrity of the inorganic inner layer during lithium plating and stripping. The C-SEI modified lithium anode shows a dendrite-free performance and stable cycle over 1200 h, with an ultralow overpotential (15 mV) at 1 mA cm^-2 in this study. This novel approach also enhances the stability of capacity retention rate by 62.3% after 100 cycles even in anode-free full cells (C-SEI@Cu||LFP). Our findings suggest a feasible strategy for addressing the instability inherent in SEI, showing great prospects for the practical application of lithium metal batteries.

Spatially Confined LiF Nanoparticles in an Aligned Polymer Matrix as the Artificial SEI Layer for Lithium Metal Anodes

The uncontrollable growth of lithium (Li) dendrites and the instability of the Li/electrolyte interface hinder the development of next-generation rechargeable lithium metal batteries. The combination of inorganic nanoparticles and polymers as the artificial SEI layer shows great potential in regulating lithium-ion flux. Here, we design spatially confined LiF nanoparticles in an aligned polymer matrix as the artificial SEI layer. A high dielectric polymer matrix homogenizes the electric field near the surface of lithium metal. Aligned pores with LiF nanoparticles promote the lithium-ion transport across the artificial SEI layer. The synergistic effect of the highly polar β-phase PVDF and LiF nanoparticles provides high stability over 900 h for the Li//Li symmetrical cell. Besides, a Li//LFP full battery equipped with this artificial layer shows good performance in the commercial carbonate electrolyte, demonstrating the great potential of this protective film in lithium metal batteries.

Constructing robust polymer/two-dimensional Ti3C2TX solid-state electrolyte interphase via in-situ polymerization for high-capacity long-life and dendrite-free lithium metal anodes

We constructed an artificial polymer/two-dimensional Ti₃C₂T_X (MXene) solid electrolyte interphase (SEI) on a Li metal surface via an in-situ polymerization strategy. The polymer layer provides excellent interface contact and outstanding adaptability for the volume expansion of Li metal, decreasing interface impedance. On the other hand, the two-dimensional MXene with a low Li nucleation energy barrier is beneficial for uniform Li deposition and restraint of interfacial side reactions. In this work, a dense and durable MXene-integrated SEI between the Li metal anode and solid-state electrolyte (SSE) interface is constructed to render the Li/SSE/Li cell to maintain a stable polarization voltage of approximately 50 mV at a capacity of 0.50 mAh cm^-2 for over 1000 h. It enables the Li/SSE/LiFePO₄ cell to deliver a capacity of 130.1 mAh g^-1 at 1C with a capacity retention of 91.4% after 900 cycles. Therefore, we believe that this facile in-situ polymerization method for constructing a layer of polymer/MXene SEI at the interface between Li metal anodes and SSE can promote the practical applications of Li metal batteries.

Lithiophilic onion-like carbon spheres as lithium metal uniform deposition host

Lithium metal is considered as a promising anode material for next-generation secondary batteries, owing to its high theoretical specific capacity (3860 mA h g^-1). Nevertheless, the practical application of Li in lithium metal batteries (LMBs) is hampered by inhomogeneous Li deposition and irreversible "dead Li", which lead to low coulombic efficiency (CE) and safe hazards. Designing unique lithiophilic structure is an efficient strategy to control Li uniformly plating /stripping. Here, we report the silver (Ag) nanoparticles coated with nitrogen-doped onion-like carbon microspheres (Ag@NCS) as a host to reduce the nucleation overpotential of Li for dendrite-free LBMs. The Ag@NCS were prepared by a simple one-step injection pyrolysis. The lithiophilic Ag is demonstrated to be priority selective deposition of Li in the carbon cage. Meanwhile, the onion-like structure benefits to uniform lithium nucleation and dendrite-free lithium during cycling. Impressively, we successfully captured lithium metal on different hosts at atomic scale, further proving that Ag@NCS can effectively and uniformly deposit Li. Besides, Ag@NCS show a superiorly electrochemical performance with a low nucleation overpotential (∼1 mV), high CE and stable cycling performance (over 400 cycles at 0.5 mA cm^-2) compared to the Ag-free onion-like carbon in LMBs. Even under harsh conditions (1 mA cm^-2, 4 mA h cm^-2), Ag@NCS still present superior cycling stability for more than 150 cycles. Furthermore, a full cell composed of LiFePO₄ cathode exhibits significantly improved voltage hysteresis with low voltage polarization. This work provides a new choice and route for the design and preparation of lithiophilic host materials.

Lithiophilic hollow Co3[Co(CN)6]2 embedded carbon nanotube film for dendrite-free lithium metal anodes

Lithium metal is considered to be an ideal anode material due to its ultra-high theoretical capacity and extremely low electric potential. Unfortunately, the infinite volume expansion and unregulated formation of lithium dendrites in the plating/stripping process restrict its practical utilization. Herein, we designed a hollow Co₃[Co(CN)₆]₂ (CoCoPBA) embedded high-conductivity carbon film as a three-dimensional (3D) lithiophilic current collector (h-CoCoPBAs@SWCNT). The interwoven carbon nanotubes with hollow nanoparticles can effectively promote electron transfer and reduce local current density, adapting to the huge volume expansion in long-term electrochemical cycling. At the same time, lithiophilic hollow CoCoPBA nanoparticles provide abundant active sites due to their large surface area, efficiently reducing nucleation overpotential and making lithium deposition easier and more uniform, both confirmed by theoretical calculation and experiment. Accordingly, compared with bare Cu electrodes, h-CoCoPBAs@SWCNT electrodes have a flat and uniform Li deposition morphology, which is beneficial to enhance the cycle life of lithium metal anodes. And the symmetrical cell assembled by h-CoCoPBAs@SWCNT shows stable cycling performance of more than 500 h at 2 mA cm^-2 with 1 mAh cm^-2. Besides, the assembled lithium-sulfur full cell also has higher cycle stability and rate performance.

Facile synthesis of hierarchical MoS2/ZnS @ porous hollow carbon nanofibers for a stable Li metal anode

Lithium metal is considered as an ideal anode candidate for next generation Li battery systems since its high capacity, low density, and low working potential. However, the uncontrollable growth of Li dendrites and infinite volume expansion impede the commercialized applications of Li-metal anodes. In this work, we rationally designed and constructed a hierarchical porous hollow carbon nanofiber decorated with diverse metal sulfides (MS-ZS@PHC). This composite scaffold has three advantages: First, the synergistic effect of multiple-size lithiophilic phases (nano ZnS and micro MoS₂) can regulate Li ions nuclei and grow up homogenously on the scaffold. Second, the enlarged interplanar spacing of MoS₂ microsphere on the fibers can provide abundant channels for Li ions transportation. Third, the porous scaffold can confine the volume expansion of Li metal anode during cycling. Therefore, in a symmetrical cell, the MS-ZS@PHC host presents a homogenous Li plating/stripping behavior and runs steadily for 1100 h at 5 mA cm^-2 with a capacity of 5 mAh cm^-2 and even for 700 h at 10 mA cm^-2 with a capacity of 1 mAh cm^-2. A full cell using MS-ZS@PHC /Li composite as anode and coupled with LiFePO₄ as cathode delivers an excellent cyclic and rate performances.

Morphologically and chemically regulated 3D carbon for Dendrite-free lithium metal anodes by a plasma processing

For the high theoretical specific capacity and low redox potential, lithium (Li) metal is considered as one of the most promising anode materials for the next generation of rechargeable batteries. In this work, we have developed an effective and accurate plasma strategy to regulate the surface morphology and functional groups of three-dimensional nitrogen-containing carbon foam (CF) to control the Li nucleation and growth. Besides the rougher surface induced by oxygen (O₂) plasma, the conversion of carbon-nitrogen chemical bond (CN), namely, change from the quaternary N to pyrrolic/pyridinic N was realized by the nitrogen (N₂) plasma. This chemical regulation of nitrogen boosts the lithiophilicity of carbon foam, which is evidenced by lower overpotential obtained from the experiment and higher binding energy for Li ions (Li⁺) calculated by density functional theory (-1.43, -1.85, -2.41 and -2.45 eV for the amorphous C-, C-quaternary N-, C-pyrrolic N- and C-pyridinic N-, respectively). The electrochemical performance of the half cells and full cells based on this plasma regulated carbon foam collectors also proved the prominent effectiveness of this plasma strategy on guiding the uniform dispersion of Li⁺ and thus inducing the homogeneous Li nucleation, as well as suppressing the growth of Li dendrites.

Strategic Approaches to the Dendritic Growth and Interfacial Reaction of Lithium Metal Anode

Utilization of lithium (Li) metal anode is highly desirable for achieving high energy density batteries. Even so, the unavoidable features of Li dendritic growth and inactive Li are still the main factors that hinder its practical application. During plating and stripping, the solid electrolyte interphase (SEI) layer can provide passivation, playing an important role in preventing direct contact between the electrolyte and the electrode in Li metal batteries. Because of complexities of the electrolyte chemical and electrochemical reactions, the various formation mechanisms for the SEI are still not well understood. What we do know is that a strategic artificial SEI achieved through additives electrolyte can suppress the Li dendrites. Otherwise, the dendrites keep generating an abundance of irreversible Li, resulting in severe capacity loss, internal short-circuiting, and cell failure. In this minireview, we focus on the phenomenon of dendritic Li-growth and provide a brief overview of SEI formation. We finally provide some clear insights and perspectives toward practical application of Li metal batteries.

A Rigid-Flexible Protecting Film with Surface Pits Structure for Dendrite-Free and High-Performance Lithium Metal Anode

An artificial organic/inorganic composite protecting film for lithium metal anode with one-side surface pits structure was prepared by poly(vinylidene fluoride-co-hexafluoropropylene) and Al₂O₃+LiNO₃ inorganic additives. Due to the unique surface structure, the composite film can not only serve as an artificial protective film, but also act as an additional lithium plating host, which synergistically enabled the lithium metal anode to adapt to high current densities meanwhile maintain dendrite-free during long-term cycling. As a result, the protected lithium metal anode can operate stably for 1000 h at a high current density of 10.0 mA cm^-2. When paired with a LiFePO₄ or sulfur cathode, the full cells with unflooded electrolyte showed significantly improved cycling performance, demonstrating great potential of this artificial protecting film in lithium metal batteries.

Amorphous-Carbon-Coated 3D Solid Electrolyte for an Electro-Chemomechanically Stable Lithium Metal Anode in Solid-State Batteries

The use of solid-state electrolyte may be necessary to enable safe, high-energy-density Li metal anodes for next-generation energy storage systems. However, the inhomogeneous local current densities during long-term cycling result in instability and detachment of the Li anode from the electrolyte, which greatly hinders practical application. In this study, we report a new approach to maintain a stable Li metal | electrolyte interface by depositing an amorphous carbon nanocoating on garnet-type solid-state electrolyte. The carbon nanocoating provides both electron and ion conducting capability, which helps to homogenize the lithium metal stripping and plating processes. After coating, we find the Li metal/garnet interface displays stable cycling at 3 mA/cm² for more than 500 h, demonstrating the interface's outstanding electro-chemomechanical stability. This work suggests amorphous carbon coatings may be a promising strategy for achieving stable Li metal | electrolyte interfaces and reliable Li metal batteries.

A multifunctional Cu6Sn5 interface layer for dendritic-free lithium metal anode

The unstable electrode/electrolyte interface of the lithium metal anode is one of the reasons that induce the formation of lithium (Li) dendrites. The Li dendrites will reduce the coulombic efficiency, and even pierce the separator to cause the safety problems. Herein, a tightly bonded and uniformly distributed Cu₆Sn₅ interface layer is formed on the surface of the Cu foam by a simple electroless plating method. The composite layer has multiple functions, such as high lithiophilicity, high carrier transport and high adaptability to mechanical strain. Based on the versatility of the Cu₆Sn₅ interface layer, the cycle life of Cu foam is increased from 150 h to 1000 h, and the deposition overpotential is as low as 18 mV. In-situ online observation proves that the existence of composite layer can make Li metal uniformly deposited to avoid the dendrites. Furthermore, Cu₆Sn₅@Cu foam also shows a higher capacity retention rate (increased from 65.2% to 78.6% after 300 cycles) and a more stable rate performance when it is used in full batteries. Compared with the single function improvement strategy proposed by the current lithium metal anode research. The Cu₆Sn₅ multifunctional composite layer modification method in this work provides a new strategy for constructing a stable electrode/electrolyte interface.

A high efficiency electrolyte enables robust inorganic-organic solid electrolyte interfaces for fast Li metal anode

Developing a high-rate Li metal anode with superior reversibility is a prerequisite for fast-charging Li metal batteries. However, the build-up of large concentration gradients under high current density leads to inhomogeneous Li deposition and unstable passivation layers of Li metal, resulting in lower Coulombic efficiency. Here we report a concentrated dual-salts LiFSI-LiNO₃/DOL electrolyte to improve the high-rate performance of Li metal anode. Sufficient Li salts help passivate the fresh Li deposition quickly. Further, DOL contributes to the formation of flexible organic layers that can accommodate the rapid volume change of Li metal upon cycling. Li metal in the electrolyte remains stable over 240 cycles with the average Coulombic efficiency of 99.14% under a high current density of 8.0 mA cm^-2.

Low-temperature fusion fabrication of Li-Cu alloy anode with in situ formed 3D framework of inert LiCux nanowires for excellent Li storage performance

The commercialization of rechargeable Li metal batteries is hindered by dendrite growth and volumetric variation. Herein, we report a Li-rich dual-phase Li-Cu alloy with built-in 3D conductive skeleton to replace conventional planar Li anode. The Li-Cu alloy is simply prepared by fusion of Li and Cu metals at a relatively low-temperature of 500 °C, followed by a cooling process where phase-segregation leads to metallic Li phase distributed in the network of LiCu_x solid solution phase. Different from the common Li alloy, the electrochemical alloying reaction between Li and Cu metals is not observed. Therefore, the lithiophilic LiCu_x nanowires guides conformal plating of Li and the porous framework provides superior dimensional stability for the anode. This unique ferroconcrete-like structure of Li-Cu alloy enables dendrite-free Li plating for an expanded cycling lifetime. Constructing a new type of Li alloy with in situ formed electrochemically inactive framework is a promising and easily scaled-up strategy toward practical application of Li metal anodes.

A polymeric composite protective layer for stable Li metal anodes

Lithium (Li) metal is a promising anode for high-performance secondary lithium batteries with high energy density due to its highest theoretical specific capacity and lowest electrochemical potential among anode materials. However, the dendritic growth and detrimental reactions with electrolyte during Li plating raise safety concerns and lead to premature failure. Herein, we report that a homogeneous nanocomposite protective layer, prepared by uniformly dispersing AlPO₄ nanoparticles into the vinylidene fluoride-co-hexafluoropropylene matrix, can effectively prevent dendrite growth and lead to superior cycling performance due to synergistic influence of homogeneous Li plating and electronic insulation of polymeric layer. The results reveal that the protected Li anode is able to sustain repeated Li plating/stripping for > 750 cycles under a high current density of 3 mA cm^-2 and a renders a practical specific capacity of 2 mAh cm^-2. Moreover, full-cell Li-ion battery is constructed by using LiFePO₄ and protected Li as a cathode and anode, respectively, rendering a stable capacity after 400 charge/discharge cycles. The current work presents a promising approach to stabilize Li metal anodes for next-generation Li secondary batteries.

Waterproof lithium metal anode enabled by cross-linking encapsulation

Lithium (Li) metal is considered as the ultimate anode choice for developing next-generation high-energy batteries. However, the poor tolerance against moist air and the unstable solid electrolyte interphases (SEI) induced by the intrinsic high reactivity of lithium bring series of obstacles such as the rigorous operating condition, the poor electrochemical performance, and safety anxiety of the cell, which to a large extent hinder the commercial utilization of Li metal anode. Here, an effective encapsulation strategy was reported via a facile drop-casting and a following heat-assisted cross-linking process. Benefiting from the inherent hydrophobicity and the compact micro-structure of the cross-linked poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP), the as-encapsulated Li metal exhibited prominent stability toward moisture, as well corroborated by the evaluations both under the humid air at 25 °C with 30% relative humidity (RH) and pure water. Moreover, the encapsulated Li metal anode exhibits a decent electrochemical performance without substantially increasing the cell polarization due to the uniform and unblocked ion channels, which originally comes from the superior affinity of the PVDF-HFP polymer toward non-aqueous electrolyte. This work demonstrates a novel and valid encapsulation strategy for humidity-sensitive alkali metal electrodes, aiming to pave the way for the large-scale and low-cost deployment of the alkali metal-based high-energy-density batteries.

Lithiophilic Zn Sites in Porous CuZn Alloy Induced Uniform Li Nucleation and Dendrite-free Li Metal Deposition

Three-dimensional (3D) lithiophilic host is one of the most effective ways to regulate the Li dendrites and volume change in working Li metal anode. The state-of-the-art 3D lithiophilic hosts are facing one main challenge in that the lithiophilic layer would melt or fall off in high-temperature environment when using the thermal infusion method. Herein, a 3D porous CuZn alloy host containing anchored lithiophilic Zn sites is employed to prestore Li using the thermal infusion strategy, and a 3D composite Li is thus fabricated. Benefiting from the lithiophilic Zn sites with a strong adsorption capacity with Li, which is based on the analyses of the nucleation overpotential, binding energy calculation, and the operando optical observation of Li plating/stripping behaviors, facile uniform Li nucleation and dendrite-free Li deposition could be achieved in the interior of the 3D porous CuZn alloy host and the 3D composite Li shows remarkable enhancement in electrochemical performance.

Nucleation and Early Stage Growth of Li Electrodeposits

The morphologies that metal electrodeposits form during the earliest stages of electrodeposition are known to play a critical role in the recharge of electrochemical cells that use metals as anodes. Here we report results from a combined theoretical and experimental study of the early stage nucleation and growth of electrodeposited lithium at liquid-solid interfaces. The spatial characteristics of lithium electrodeposits are studied via scanning electron microscopy (SEM) in tandem with image analysis. Comparisons of Li nucleation and growth in multiple electrolytes provide a comprehensive picture of the initial nucleation and growth dynamics. We report that ion diffusion in the bulk electrolyte and through the solid electrolyte interphase (SEI) formed spontaneously on the metal play equally important roles in regulating  Li nucleation and growth. We show further that the underlying physics dictating bulk and surface diffusion are similar across a range of electrolyte chemistries and measurement conditions, and that fluorinated electrolytes produce a distinct flattening of Li electrodeposits at low rates. These observations are rationalized using X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and contact angle goniometry to probe the interfacial chemistry and dynamics. Our results show that high interfacial energy and high surface ion diffusivity are necessary for uniform Li plating.

An air-stable and waterproof lithium metal anode enabled by wax composite packaging

The reviving use of lithium metal anode (LMA) is one of the most promising ways to upgrade the energy density of lithium ion batteries. In the roadmap towards the real use, besides the formation of the dendrite, various adverse reactions due to the high activity of LMA when exposed to air or the electrolyte limit its practical applications. Learning from the packaging technology in electronic industry, we propose a wax-based coating compositing with the ion conducting poly (ethylene oxide) by a simple dip-coating technology and the prepared LMA is featured with an air-stable and waterproof surface. The LMA thus remains stable for 24 h in ambient air even with the relative humidity of 70% while retaining about 85% its electrochemical capacity. More importantly, the LMA is accessible to water and when dipping in water, no obvious adverse reactions or capacity decay is observed. With the composite coating, a steady cycling performance for 500 h in symmetrical cells and a low capacity decay rate of 0.075% per cycle after 300 cycles in lithium-sulfur batteries assembled with the packaged anode have been achieved. This work demonstrates a very simple and effective LMA package technology which is easily scalable and is very promising for speeding up the industrialization of lithium-sulfur batteries and shows potentials for the large-scale production of air-sensitive electrode materials not limited to LMAs.

Lithium Plating and Stripping on Carbon Nanotube Sponge

Lithium metal is an ideal anode material due to its high specific capacity and low redox potential. However, issues such as dendritic growth and low Coulombic efficiency prevent its application in secondary lithium batteries. The use of three-dimensional (3D) porous current collector is an effective strategy to solve these problems. Herein, commercial carbon nanotube (CNT) sponge is used as a 3D current collector for dendrite-free lithium metal deposition to improve the Coulombic efficiency and the cycle stability of the lithium metal batteries. The high specific surface area of the CNT increases the density of the lithium nucleation sites and ensures the uniform lithium deposition while the "pre-lithiation" behavior of the porous CNT enhances its affinity with the deposited lithium. Meanwhile, the lithium plating/stripping on the sponge maintains high Coulombic efficiency and high cycling stability due to the robust structure of graphitic-amorphous carbon composite in the ether-based electrolyte. Our findings exhibit the feasibility of using CNT sponge as a 3D porous current collector for lithium deposition. They shed light on designing and developing advanced current collectors for the lithium metal electrode and will promote the commercialization of the secondary lithium batteries.

Poor Man's Atomic Layer Deposition of LiF for Additive-Free Growth of Lithium Columns

Lithium metal is an ideal material for high-energy, cost-effective rechargeable energy storage systems. The thermodynamically unfavorable solid-liquid interface between the lithium metal and organic electrolyte necessitates the formation of an interlayer (SEI) which is known to have significant impact on lithium morphologies. Less well understood is the impact of the current collector substrate on the morphology of electrodeposited lithium. Here we report on the morphology of electrodeposited lithium as a function of the chemical pretreatments of the working electrode. We find that a copper substrate pretreatment with acidic solutions (sulfuric, oxalic, or acetic acid) results in the deposition of close-packed lithium columns with a uniform diameter. A controlled study of the pre-electrodeposited copper surface indicates that the formation of a 5-8 nm thick LiF protective layer on copper substrate from a chemical reaction between adsorbed surface water layer in acidic solutions and LiPF₆ electrolyte is the key process in the electrochemical growth of lithium columns. We anticipate that this simple chemical approach can be generalized as a scalable, low-cost, additive-free substrate treatment method for depositing a LiF protective layer, broadly applicable in the development of uniform lithium films.

Lithium Dendrite Suppression and Enhanced Interfacial Compatibility Enabled by an Ex Situ SEI on Li Anode for LAGP-Based All-Solid-State Batteries

The electrode-electrolyte interface stability is a critical factor influencing cycle performance of All-solid-state lithium batteries (ASSLBs). Here, we propose a LiF- and Li₃N-enriched artificial solid state electrolyte interphase (SEI) protective layer on metallic lithium (Li). The SEI layer can stabilize metallic Li anode and improve the interface compatibility at the Li anode side in ASSLBs. We also developed a Li_1.5Al_0.5Ge_1.5(PO₄)₃-poly(ethylene oxide) (LAGP-PEO) concrete structured composite solid electrolyte. The symmetric Li/LAGP-PEO/Li cells with SEI-protected Li anodes have been stably cycled with small polarization at a current density of 0.05 mA cm^-2 at 50 °C for nearly 400 h. ASSLB-based on SEI-protected Li anode, LAGP-PEO electrolyte, and LiFePO₄ (LFP) cathode exhibits excellent cyclic stability with an initial discharge capacity of 147.2 mA h g^-1 and a retention of 96% after 200 cycles.

Recent developments of aprotic lithium-oxygen batteries: functional materials determine the electrochemical performance

Lithium oxygen battery has the highest theoretical capacity among the rechargeable batteries and it can reform energy storage technology if it comes to commercialization. However, many critical challenges, mainly embody as low charge/discharge round-trip efficiency and poor cycling stability, impede the development of Li-O₂ batteries. The electrolyte decomposition, lithium metal anode corrosion and sluggish oxygen reaction kinetics at cathode are all responsible for poor electrochemical performances. Particularly, the catalytic cathode of Li-O₂ batteries, playing a crucial role to reduce the oxygen during discharging and to decompose discharge products during charging, is regarded as a breakthrough point that has been comprehensive investigated. In this review, the progress and issues of electrolyte, anode and cathode, especially the catalysts used at cathode, are systematically summarized and discussed. Then the perspectives toward the developments of a long life Li-O₂ battery are also presented at last.

Nanoscale Nucleation and Growth of Electrodeposited Lithium Metal

Lithium metal has re-emerged as an exciting anode for high energy lithium-ion batteries due to its high specific capacity of 3860 mAh g^-1 and lowest electrochemical potential of all known materials. However, lithium has been plagued by the issues of dendrite formation, high chemical reactivity with electrolyte, and infinite relative volume expansion during plating and stripping, which present safety hazards and low cycling efficiency in batteries with lithium metal electrodes. There have been a lot of recent studies on Li metal although little work has focused on the initial nucleation and growth behavior of Li metal, neglecting a critical fundamental scientific foundation of Li plating. Here, we study experimentally the morphology of lithium in the early stages of nucleation and growth on planar copper electrodes in liquid organic electrolyte. We elucidate the dependence of lithium nuclei size, shape, and areal density on current rate, consistent with classical nucleation and growth theory. We found that the nuclei size is proportional to the inverse of overpotential and the number density of nuclei is proportional to the cubic power of overpotential. Based on this understanding, we propose a strategy to increase the uniformity of electrodeposited lithium on the electrode surface.

Polymer nanofiber-guided uniform lithium deposition for battery electrodes

Lithium metal is one of the most promising candidates as an anode material for next-generation energy storage systems due to its highest specific capacity (3860 mAh/g) and lowest redox potential of all. The uncontrolled lithium dendrite growth that causes a poor cycling performance and serious safety hazards, however, presents a significant challenge for the realization of lithium metal-based batteries. Here, we demonstrate a novel electrode design by placing a three-dimensional (3D) oxidized polyacrylonitrile nanofiber network on top of the current collector. The polymer fiber with polar surface functional groups could guide the lithium ions to form uniform lithium metal deposits confined on the polymer fiber surface and in the 3D polymer layer. We showed stable cycling of lithium metal anode with an average Coulombic efficiency of 97.4% over 120 cycles in ether-based electrolyte at a current density of 3 mA/cm(2) for a total of 1 mAh/cm(2) of lithium.

Ultrathin two-dimensional atomic crystals as stable interfacial layer for improvement of lithium metal anode

Stable cycling of lithium metal anode is challenging due to the dendritic lithium formation and high chemical reactivity of lithium with electrolyte and nearly all the materials. Here, we demonstrate a promising novel electrode design by growing two-dimensional (2D) atomic crystal layers including hexagonal boron nitride (h-BN) and graphene directly on Cu metal current collectors. Lithium ions were able to penetrate through the point and line defects of the 2D layers during the electrochemical deposition, leading to sandwiched lithium metal between ultrathin 2D layers and Cu. The 2D layers afford an excellent interfacial protection of Li metal due to their remarkable chemical stability as well as mechanical strength and flexibility, resulting from the strong intralayer bonds and ultrathin thickness. Smooth Li metal deposition without dendritic and mossy Li formation was realized. We showed stable cycling over 50 cycles with Coulombic efficiency ∼97% in organic carbonate electrolyte with current density and areal capacity up to the practical value of 2.0 mA/cm(2)and 5.0 mAh/cm(2), respectively, which is a significant improvement over the unprotected electrodes in the same electrolyte.