Solid Electrolyte Interface Research Articles

Quasi Solid Polyzwitterion- Polyacrylamide Electrolytes for Rechargeable Zinc-Ion Battery

Zinc-ion batteries have attracted significant attention due to their low cost, rechargeability, and superior safety features. In fact, the use of aqueous electrolytes negatively affects battery performance due to the solid electrolyte interface (SEI), creating zinc corrosion, hydrogen evolution reaction (HER), and dendrite formation. To address these challenges, quasi-solid electrolytes (QSE) based on polyacrylamide-poly (3-(1-vinyl-3-imidazolio) propanesulfonate) (PAM/PVIPS) have been developed. PAM stands out as matrix QSE due to its excellent flexibility and electrochemical stability. PVIPS offers a well-defined pathway for ion transportation caused by cationic and anionic groups in structure. Clearly, the asymmetrical zinc cell with PAM/PVIPS QSE effectively reduces the overpotential profile, prolongs the stabilized zinc plating/stripping and enhances ionic conductivity, compared to PAM QSE. Additionality, the performance of Zn||δ-MnO2 is also enhanced with PAM/PVIPS QSE, yielding the specific capacity value of 65 mAh g-1, which is superior to the pristine PAM QSE (56 mAh g-1).

LiTFSI salt concentration effect for well‐balanced ion transport and physical properties in nanocellulose‐reinforced PEO#600 solid electrolytes

AbstractPoly(ethylene oxide) (PEO) with an oxygen group serves as a reactive site for the pathway of lithium‐ion transport. Reducing the PEO crystal domain in solid electrolytes is an extremely efficient approach for enhancing the mobility of ions. The present study applied various EO/Li molar ratios to modify the physical and electrochemical properties of PEO nanocomposite reinforced by nanocellulose. An elevated lithium salt concentration causes a gradual decline in crystallinity and mechanical strength. The electrochemical performance of the 13 EO/Li molar ratio voltammogram and charge–discharge shows efficient Li‐ion transport with 5.6 × 10−4 S/cm conductivity at room temperature and 131 mA h g−1 initial discharge capacity. The shifting glass transition and melting point at lower temperatures (−40.5 to −44.5°C and 45.3–43.8°C) suggest greater ion mobility throughout the large non‐crystalline structure. Lithium ions are limited by membrane weakening and re‐crystallization caused by high lithium salt (EM_11) concentrations. EM_13 has the highest specific capacity, operating voltage, and lithium transfer number depends on balanced electrochemical performance and physical features. XPS surface chemistry analysis explains LiF, Li2CO3, and Li2O solid electrolyte interfaces (SEI) in EM samples. A lower Li2O (11.62 at.%) than LiF (38.4 at.%) after cycling enhances Li‐ion diffusion and cell reversibility.

Magnetic Field Enable Lithium Ions to Penetrate Lithophilic 3D Collectors and Enhance Electrochemical Performance

Abstract Lithium metal batteries, celebrated for their exceptional energy density, are promising for advanced energy storage. Nevertheless, the dynamic deformation of lithium metal during cycling often leads to the unchecked proliferation of lithium dendrites, compromising the solid electrolyte interface. This not only deteriorates cycle stability but also poses significant safety risks. In our approach, we develop a three-dimensional lithium-affinitive composite current collector, utilizing an external magnetic field. The lithiophilic nature of V2O5, coupled with the deformability support provided by nickel foam and the depth-enhancing influence of the magnetic field on lithium metal deposition, collectively contribute to a more controlled and stable lithium environment. Our findings indicate that this novel setup allows for a lithium metal deposition depth of up to 310 μm, markedly curtailing the growth of dendrites in successive cycles. Remarkably, batteries reassembled with this magnetically-enhanced, lithium pre-deposited current collector exhibits a coulombic efficiency of 98.3% after 320 cycles at 1 mA cm-2. Moreover, a full cell, equipped with LiFePO4, delivers an initial capacity of 158.4 mAh g-1 at 1 C.

Weakly solvated electrolyte enables the robust solid electrolyte interface on SiOx anodes for lithium-ion battery

Silicon oxide (SiOx) anodes are considered to be the promising alternative to graphite anodes for lithium-ion batteries. However, the traditional carbonate electrolyte fails to generate the effective solid electrolyte interface (SEI) on SiOx anodes to well adapt the large volume expansion of SiOx particles. Herein, a weakly solvated perfluorinated electrolyte with dual lithium salts was designed to match SiOx anodes. The perfluorinated solvent with weakened solvation ability and the strong coordination of Li+-DFOB− and Li+-TFSI− lead to an anion-dominated solvated shell, which induces the formation of inorganics-rich SEI. The high-strength bonds (Li-F, B-F, B-O, B-N et al.) enable high mechanical strength and rapid ion migration of the SEI film, thereby effectively accommodating the volume expansion of SiOx and avoiding continuous decomposition of the electrolyte. Furthermore, as designed electrolyte also shows excellent flame retardancy and high voltage stability. Consequently, the SiOx anode exhibits remarkably improved cycling performance in contrast to that in traditional carbonate electrolyte, maintaining 1073.7 mAh/g after 300 cycles at 1.0 A/g when paired with metal Li, and presents excellent compatibility with commercial cathodes including LiFePO4 and LiNi0.8Co0.1Mn0.1O2. This work provides a new inspiration and path for the design of electrolyte highly matched with silicon oxide anodes.

Co-solvent electrolyte-induced zinc anode surface reconstruction for high performance zinc ion batteries

The progress of rechargeable zinc (Zn) ion batteries (RZBs) has been significantly impeded by the occurrence of side reactions and dendritic issues on Zn anodes, which are attributed to the intricate reaction kinetics observed in aqueous electrolytes. Herein, we propose a co-solvent electrolyte comprising a combination of N, N-dimethylformamide (DMF) and Dimethyl sulfoxide (DMSO). This electrolyte reconstructs the surface of the Zn anode and generates a dense and robust solid electrolyte interface (SEI), which promotes uniform Zn2+ deposition and enhances Zn2+ transport kinetics. The DFT further shows that the electrolyte has a unique solvated structure which enables uniform Zn2+ deposition and the creation of stable SEI. By utilizing these advantages, the co-solvent electrolyte is capable of enduring uninterrupted cycling for more than 4000 h at a current density of 1 mA cm−2, and for over 2000 h at a current density of 5 mA cm−2. Furthermore, the Zn||NH4V4O10 full cell demonstrated exceptional electrochemical performance with regard to charge/discharge capacity and cycle stability. This study showcases the effectiveness of non-aqueous electrolytes, which will enable the progress of secure and high-capacity RZBs.

Trace Amounts of Multifunctional Electrolyte Additives Enhance Cyclic Stability of High-Rate Aqueous Zinc-Ion Batteries.

Aqueous zinc ion batteries (AZIBs) are renowned for their exceptional safety and eco-friendliness. However, they face cycling stability and reversibility challenges, particularly under high-rate conditions due to corrosion and harmful side reactions. This work introduces fumaric acid (FA) as a trace amount, suitable high-rate, multifunctional, low-cost, and environmentally friendly electrolyte additive to address these issues. FA additives serve as prioritized anchors to form water-poor Inner Helmholtz Plane on Zn anodes and adsorb chemically on Zn anode surfaces to establish a unique in situ solid-electrolyte interface. The combined mechanisms effectively inhibit dendrite growth and suppress interfacial side reactions, resulting in excellent stability of Zn anodes. Consequently, with just tiny quantities of FA, Zn anodes achieve a high Coulombic efficiency (CE) of 99.55 % and exhibit a remarkable lifespan over 2580 hours at 5mA cm-2, 1 mAh cm-2 in Zn//Zn cells. Even under high-rate conditions (10mA cm-2, 1 mAh cm-2), it can still run almost for 2020 hours. Additionally, the Zn//V2O5 full cell with FA retains a high specific capacity of 106.95 mAh g-1 after 2000 cycles at 5 A g-1. This work provides a novel additive for the design of electrolytes for high-rate AZIBs.

MgF2 Interface Engineering Promotes the Growth and Stability of LiF-Rich Solid-Electrolyte Interphases on Si-C.

Volume expansion of the Si-C anode during the charging/discharging process causes continuous fracture/formation of the solid electrolyte interface (SEI), which leads to rapid capacity fading. Here, we designed a MgF2-modified separator (MF-PP) to construct a fluorine-rich SEI layer by generating more LiF. The robust SEI layer formed can alleviate the volume stress and prevent crack growth in Si-C electrodes. After 450 cycles, the Si-C||MF-PP half cell retained a reversible capacity of 543.2 mAh g-1, while the LFP||MF-PP||Si-C full cell maintained a reversible capacity of 103.4 mAh g-1 with high Coulombic efficiency after 100 cycles. This facile and low-cost separator modification strategy provides an easily scalable approach to develop stable Si-based anodes for next-generation high-energy-density systems.

Stabilization Strategies of Lithium Metal Anode Toward Dendrite-Free Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are considered as a most promising rechargeable lithium metal batteries because of their high energy density and low cost. However, the Li-S batteries mainly suffer the capacity decay issue caused by the shutting effect of lithium polysulfides and the safety issues arising from the Li dendrites formation. This review outlines the current issues of Li-S batteries. Furthermore, we comprehensively summarized the challenges encountered by Li anode in Li-S batteries, such as the heterogeneous deposition of the Li anode, the unstable solid electrolyte interface (SEI) layer, and volume expansion. Moreover, research progresses in the stabilization strategies of Li anodes (physical approaches, optimization of electrolyte, surface protection layer, and design of current collector) is discussed in detail. Lastly, the remaining challenges and future research directions of Li metal anode stabilization in Li-S batteries are also present.

Vertically Fluorinated Graphene Encapsulated SiOx Anode for Enhanced Li+ Transport and Interfacial Stability in High-Energy-Density Lithium Batteries.

Achieving high energy density has always been the goal of lithium-ion batteries (LIBs). SiOx has emerged as a compelling candidate for use as a negative electrode material due to its remarkable capacity. However, the huge volume expansion and the unstable electrode interface during (de)lithiation, hinder its further development. Herein, we report a facile strategy for the synthesis of surface fluorinated SiOx (SiOx@vG-F), and investigate their influences on battery performance. Systematic experiments investigations indicate that the reaction between Li+ and fluorine groups promotes the in situ formation of stable LiF-rich solid electrolyte interface (SEI) on the surface of SiOx@vG-F anode, which effectively suppresses the pulverization of microsized SiOx particles during the charge and discharge cycle. As a result, the SiOx@vG-F enabled a higher capacity retention of 86.4 % over 200 cycles at 1.0 C in the SiOx@vG-F||LiNi0.8Co0.1Mn0.1O2 full cell. This approach will provide insights for the advancement of alternative electrode materials in diverse energy conversion and storage systems.

Formulating Self-Repairing Solid Electrolyte Interface via Dynamic Electric Double Layer for Practical Zinc Ion Batteries.

Zinc ion batteries (ZIBs) encounter interface issues stemming from the water-rich electrical double layer (EDL) and unstable solid-electrolyte interphase (SEI). Herein, we propose the dynamic EDL and self-repairing hybrid SEI for practical ZIBs via incorporating the horizontally-oriented dual-site additive. The rearrangement of distribution and molecular configuration of additive constructs the robust dynamic EDL under different interface charges. And, a self-repairing organic-inorganic hybrid SEI is constructed via the electrochemical decomposition of additive. The dynamic EDL and self-repairing SEI accelerate interfacial kinetics, regulate deposition and suppress side reactions in the both stripping and plating during long-term cycles, which affords high reversibility for 500 h at 42.7 % depth of discharge or 50 mA ⋅ cm-1. Remarkably, Zn//NVO full cells deliver the impressive cycling stability for 10000 cycles with 100 % capacity retention at 3 A ⋅ g-1 and for over 3000 cycles even at lean electrolyte (7.5 μL ⋅ mAh-1) and high loading (15.26 mg ⋅ cm-2). Moreover, effectiveness of this strategy is further demonstrated in the low-temperature full cell (-30 °C).

High Entropy Induced Local Charge Enhancement Promotes Frank–Van der Merwe Growth for Dendrite‐Free Potassium Metal Batteries

AbstractPotassium metal batteries (PMBs) are promising for next‐generation energy storage. However, the high reactivity of the anode causes instability in the solid electrolyte interface (SEI), resulting in Volmer‐Weber (V‐W) type deposition. To achieve uniform Frank‐van der Merwe (F‐M) type deposition, high entropy alloy nanoparticles are designed (HEA NPs) with equimolar ratios of Mn, Fe, Co, Cu, and Ni to enhance the substrate‐K metal interface. HEA NPs enhance the K affinity of the N‐doped nanocarbon fiber substrate (N‐PCNF) and maximize ion and electron transport efficiency. The dendrite‐free horizontal growth of K metal confirmed through Operando X‐ray diffraction (XRD) and optical microscopy (OM). Consequently, the asymmetric cell exhibits ultra‐long cycling stability of 2350 hours at a high current density of 8 mA cm−2. The full cell composed of molten K diffusion into HEA NPs decorated N‐PCNF anode with perylene‐3,4,9,10‐tetracarboxylic dianhydride cathode (HEA‐N‐PCNF‐K||PTCDA) delivers an energy density of 331 W h kg−1 and remains stable over 2000 cycles. This study offers a promising pathway for innovative PMBs designs with broad application prospects.

Manipulating Electrolyte Interface Chemistry Enables High-Performance TiO2 Anode for Sodium-Ion Batteries

Titanium dioxide (TiO2) has emerged as a candidate anode material for sodium-ion batteries (SIBs). However, their applications still face challenges of poor rate performance and low initial coulomb efficiency (ICE), which are induced by the unstable solid-electrolyte interface (SEI) and sluggish Na+ diffusion kinetics in conventional ester-based electrolytes. Herein, inspired by the electrode/electrolyte interfacial chemistry, tetrahydrofuran (THF) is exploited to construct an advanced electrolyte and reveal the relationship between the improved electrochemical performance and the derived SEI film on TiO2 anode. The robust and homogeneously distributed F-rich SEI film formed in THF electrolyte favors fast interfacial charge transfer dynamics and excellent interfacial stability. As a result, the THF electrolyte endows the TiO2 anode with greatly improved ICE (64.5%), exceptional rate capabilities (186 mAh g−1 at 5.0 A g−1), and remarkable cycling stability. This study elucidates the control of interfacial chemistry by rational electrolyte design and offers insights into the development of high-performance and long-lifetime TiO2 anode.

Anion Receptor-manipulated solvation chemistry and electric double layer enables high Zn-Utilization rate and lean Zn metal batteries

The practical application of aqueous Zn metal batteries (AZMBs) is impeded by inferior reversibility and stability of Zn metal anode (ZMA) originated from side reactions and dendrite growth. Herein, anion receptor l-Proline (LP) is selected to simultaneously manipulate solvation chemistry and electric double layer (EDL) for constructing dendrite-free and stable AZMBs with an ultra-high depth of discharge (DOD of 100 %) and low negative/positive capacity ratio (N/P of 1.1). Experimental and computational results demonstrate that the strong interaction between −SO32- group from OTf- anion and LP promotes the coordination effect of cation and solvent, which improves the stability of electrolyte and induces fine and uniform Zn nucleus formation. Meanwhile, the preferential reduction of OTf- and adsorption of LP establish an anion-derived ZnF2-rich solid electrolyte interface by altering EDL structure, which enhances the mechanical stability and Zn2+ diffusion kinetics of the interface and prevents the contact of H2O molecules. Consequently, ZMA in LP/Zn(OTf)2 electrolyte delivers a satisfactory cycling lifespan under DOD of 100 % and an outstanding Coulombic efficiency of 99.93 % for 10,000 cycles at 10 mA cm−2. Moreover, Zn||Od-NH4V4O10 full cells with LP/Zn(OTf)2 electrolyte demonstrate excellent cycle stability at high cathode loading (20.412 mg), low N/P (1.1), and high temperature (50 °C).

The effect of low-temperature starting on the thermal safety of lithium-ion batteries

With the widespread application of lithium-ion batteries (LIBs) in the field of energy equipment, their probability of starting or operating in low-temperature environments is also increasing. However, there is currently a lack of research on the changes in thermal safety of batteries after use in corresponding environments. In this work, the thermal safety performance, degradation mechanisms and evaluation method of LIBs at low-temperature start-up conditions are studied. The results show that starting at low temperature leads to the decrease of cell capacity. Electrochemical characterization and cell disassembly analysis indicate that the loss of active lithium ions is mainly caused by the evolution of lithium and the growth of solid electrolyte interface films. In addition, the low-temperature startup results in the decrease of thermal runaway (TR) onset temperature and the advance of TR time. In order to quantitatively evaluate the safety state of the LIBs, an evaluation model based on Informer algorithm is established. The model extracts the discharge capacity, discharge energy and dV/dQ as aging characteristic parameters, and extracts TR temperature as thermal safety characteristic parameters. The data set is processed by cubic spline interpolation. After training and verification, the accuracy of the model reaches 80 %.

Lift-Out Specimen Preparation and Multiscale Correlative Investigation of Li-Ion Battery Electrodes Using Focused Ion Beam-Secondary Ion Mass Spectrometry Platforms.

Advanced characterization is paramount to understanding battery cycling and degradation in greater detail. Herein, we present a novel methodology of battery electrode analysis, employing focused ion beam (FIB) secondary-ion mass spectrometry platforms coupled with a specific lift-out specimen preparation, allowing us to optimize analysis and prevent air contamination. Correlative microscopy, combining electron microscopy and chemical imaging of a liquid electrolyte Li-ion battery electrode, is performed over the entire electrode thickness down to subparticle domains. We observed a distinctive remnant lithiation among interparticles of the anode at the discharge state. Furthermore, chemical mapping reveals the nanometric architecture of advanced composite active materials with a lateral resolution of 16 nm and the presence of a solid electrolyte interface on the particle boundaries. We highlight the methodological advantages of studying interfaces and the ability to conduct high-performance chemical and morphological correlative analyses of battery materials and comment on their potential use in other fields.

Comparison of Construction Strategies of Solid Electrolyte Interface (SEI) in Li Battery and Mg Battery-A Review.

The solid electrolyte interface (SEI) plays a critical role in determining the performance, stability, and longevity of batteries. This review comprehensively compares the construction strategies of the SEI in Li and Mg batteries, focusing on the differences and similarities in their formation, composition, and functionality. The SEI in Li batteries is well-studied, with established strategies that leverage organic and inorganic components to enhance ion diffusion and mitigate side reactions. In contrast, the development of the SEI in Mg batteries is still in its initial stages, facing significant challenges such as severe passivation and slower ion kinetics due to the divalent nature of magnesium ions. This review highlights various approaches to engineering SEIs in both battery systems, including electrolyte optimization, additives, and surface modifications. Furthermore, it discusses the impact of these strategies on electrochemical performance, cycle life, and safety. The comparison provides insights into the underlying mechanisms, challenges, and future directions for SEI research.

Surface Science and Engineering for Electrochemical Materials.

ConspectusIn electrochemical energy storage systems, the reversible storage capacity of battery materials often degrades due to parasitic reactions at the electrode-electrolyte interface, transitional metal dissolution, and metallic dendrite growth at the surface. Surface engineering techniques offer the opportunity to modify the composition and structure of a surface, thereby enabling control over chemical reactions occurring at the surface and manipulating chemical interactions at the solid-solid or solid-liquid interface. These modifications can help stabilize the surface of electrode materials and prevent unwanted reactions with electrolytes without changing the original properties of the bulk structure. This allows for achieving full theoretical capacity and maximizing battery material capacity retention with minimal overpotentials. In the past decade, our teams have been working on developing a variety of surface engineering techniques. These include applying atomic and molecular layer deposition (ALD and MLD), templating, doping, and coating via wet-chemical processes to stabilize the surfaces of electrode materials. The aim is to mitigate parasitic side-reactions without impeding charge transfer kinetics, suppress dendrite growth, and ultimately improve the electrode performance.This Account summarizes the research conducted in our research laboratory with an aim to improve battery cycling durability and efficiency by modifying electrode surfaces. We have employed techniques such as ALD, MLD, templating, and wet-chemical processes to illustrate how the stabilized surface improves the performance of lithium-ion (Li-ion), solid-state electrolytes and magnesium-metal (Mg-metal) batteries. For instance, by applying ultrathin layers of inorganic (e.g., Al2O3) or organic-inorganic coatings (e.g., alucone, lithicone, and polyamides) to the surface of LiNixMnyCozO2 (x + y + z = 1, NMC) and silicon (Si) electrodes─usually just a few angstroms or nanometers thick─we have observed notable improvements in cycling efficiency and durability. When using ultrathick electrodes, the traditional electrode fabrication has a problem with high tortuosity, which hinders both rate capability and long-term cycling. To solve this issue, three-dimensional templates have been employed to reduce electrode tortuosity, enabling high-rate performance and long-term cycling. In the case of Mg-metal batteries, the buildup of an insulating MgO layer due to side reactions with electrolytes blocks Mg2+ ion transport, which can ultimately cause the battery to fail. To address this issue, we have developed an artificial solid-electrolyte interface using cyclized polyacrylonitrile and magnesium trifluoromethanesulfonate. This interface prevents the reduction of the carbonate electrolyte while allowing Mg2+ diffusion, ultimately boosting overall cell performance.This Account also discusses the significance of choosing suitable materials and effective surface engineering methods with the objective of enhancing surface properties while preserving the bulk properties of the electrodes. It is believed that surface modification and engineering can not only significantly improve the electrochemical performance of existing battery materials but also facilitate the development of new battery materials that were previously incompatible with current electrolytes. By highlighting these aspects, this Account underscores the transformative potential of surface modification and engineering in battery technology, paving the way for future innovations in energy storage solutions.

Thermo-electric behavior analysis and coupled model characterization of 21,700 cylindrical ternary lithium batteries affected by cyclic aging

In order to achieve a balance between the precision of thermal behavior simulation of lithium batteries affected by cyclic aging and the practicality of engineering popularization and application, a simple degraded battery thermal model needs to be constructed. In this article, a characterization approach for the coupled battery thermo-electric model affected by cyclic aging is designed. This method is suitable for simulating the thermal behavior of lithium degraded batteries with different materials and shapes under different environmental temperatures. This paper introduces the idea by taking the 21,700 cylindrical ternary lithium batteries as an example. Firstly, based on the interaction mechanism between the growth of the solid electrolyte interface film on the battery negative electrode surface at the microscopic level and the battery thermoelectric coupling characteristics at the macro level, the paper constructs a theoretical model of the degraded battery. Further, it conducts experiments to analyze the battery charging and discharging behaviors in the process of cyclic aging. Based on experimental data, this paper conducts multiple fitting calculations to extract essential modeling parameters. Subsequently, this paper builds the battery physical model in the simulation software based on the above modeling parameters. It applies the battery physical model to simulate the thermal characteristics and temperature field. Then, it conducts experiments to demonstrate the precision of the model. This paper uses the infrared imaging technique to visualize and analyze temperature field variations on the battery surface. And it uses thermocouple temperature sensors to capture the battery surface temperature changes. The simulation results are compared with the experimental data, the errors are less than 5 %. Compared with other existing battery thermal models, the model of this paper is more suitable for engineering popularization and application of thermal behavior simulation of lithium batteries affected by cyclic aging.

Unraveling chemical origins of dendrite formation in zinc-ion batteries via in situ/operando X-ray spectroscopy and imaging

To prevent zinc (Zn) dendrite formation and improve electrochemical stability, it is essential to understand Zn dendrite growth, particularly in terms of morphology and relation with the solid electrolyte interface (SEI) film. In this study, we employ in-situ scanning transmission X-ray microscopy (STXM) and spectro-ptychography to monitor the morphology evolution of Zn dendrites and to identify their chemical composition and distribution on the Zn surface during the stripping/plating progress. Our findings reveal that in 50 mM ZnSO4, the initiation of moss/whisker dendrites is chemically controlled, while their continued growth over extended cycles is kinetically governed. The presence of a dense and stable SEI film is critical for inhibiting the formation and growth of Zn dendrites. By adding 50 mM lithium chloride (LiCl) as an electrolyte additive, we successfully construct a dense and stable SEI film composed of Li2S2O7 and Li2CO3, which significantly improves cycling performance. Moreover, the symmetric cell achieves a prolonged cycle life of up to 3900 h with the incorporation of 5% 12-crown-4 additives. This work offers a strategy for in-situ observation and analysis of Zn dendrite formation mechanisms and provides an effective approach for designing high-performance Zn-ion batteries.

Hybrid conductive-lithophilic-fluoride triple protection interface engineering: Dendrite-free reverse lithium deposition for high-performance lithium metal batteries

Lithium metal batteries (LMBs) with high energy density are impeded by the instability of solid electrolyte interface (SEI) and the uncontrolled growth of lithium (Li) dendrite. To mitigate these challenges, optimizing the SEI structure and Li deposition behavior is the key to stable LMBs. This study novelty proposes a facile synthesis of MgF2/carbon (C) nanocomposite through the mechanochemical reaction between metallic Mg and polytetrafluoroethylene (PTFE) powders, and its modified polypropylene (PP) separator enhances LMB performance. The in-situ formed highly conductive fluorine-doped C species play a crucial role in facilitating ion/electron transport, thereby accelerating electrochemical kinetics and altering Li deposition direction. During cycling, the in-situ reaction between MgF2 and Li leads to the formation of LiMg alloy, along with a LiF-rich SEI layer, which reduces the nucleation overpotential and reinforces the interphase strength, leading to homogeneous Li deposition with dendrite-free feature. Benefiting from these merits, the Li metal is densely and uniformly deposited on the MgF2/C@PP separator side rather than on the current collector side. Furthermore, the symmetric cell with MgF2/C@PP exhibits superb Li plating/stripping performance over 2800 h at 1 mA cm−2 and 2 mA h cm−2. More importantly, the assembled Li@MgF2/C@PP|LiFePO4 full cell with a low negative/positive ratio of 3.6 delivers an impressive cyclability with 82.7% capacity retention over 1400 cycles at 1 C.