Li-Mg Alloy Research Articles

Trinitarian Design of Gradient Artificial Interphase Enables Colossal Granular Li Deposits for Stable Li-Metal Batteries.

The cycling lifespan of Li-metal batteries is compromised by the unstable solid electrolyte interphase (SEI) and the continuous Li dendrites, restricting their practical implementations. Given these challenges, establishing an artificial SEI holds promise. Herein, a trinitarian gradient interphase is innovatively designed through composite coatings of magnesium fluoride (MgF2), N-hexadecyltrimethylammonium chloride (CTAC), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) on Li-metal anode (LMA). Specifically, the MgF2/CTAC/PVDF-HFP SEI spontaneously forms a lithium fluoride (LiF)-rich PVDF-HFP-based SEI, along with lithium-magnesium (Li-Mg) alloy substrate as lithiophilic electronic conductor and positively charged CTAC during plating. Noticeably, the Li-Mg alloy homogenizes the distribution of electric field and reduce the internal resistance, while the electronically insulated LiF/PVDF-HFP composite SEI offers fast ion-conducting and mechanical flexibility, accommodating the volumetric expansion and ensuring stable Li-ion flux. Additionally, CTAC at the dendritic tip is pivotal for mitigating dendrites through its electrostatic shield mechanism. Innovatively, this trinitarian synergistic mechanism, which facilitates colossal granular Li deposits, constructs a dendrite-free LMA, leading to stable cycling performances in practical Li||LFP, popular Li||NCM811, and promising Li||S full cells. This work demonstrates the design of multifunctional composite SEI for comprehensive Li protection, thereby inspiring further advancements in artificial SEI engineering for alkali-metal 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.

Modeling the electro-chemo-mechanical failure at the lithium-solid electrolyte interface: Void evolution and lithium penetration

The solid-solid contact interface is crucial for the reliability of solid-state energy storage systems. The contact condition becomes more complicated when lithium (Li) metal is used as the anode. The contact between solid electrolyte (SE) and Li metal is inferior compared to the liquid/solid interface in conventional Li-ion batteries. Experimental evidence has shown that improper operating conditions of solid-state batteries can lead to electro-chemo-mechanical failures at the Li/SE interface, including the formation of voids and the penetration of Li. In this study, a unified phase-field model is developed to investigate these two mechanisms. The model considers the coupled electro-chemo-mechanical processes including void diffusion, lattice annihilation, stripping and plating reactions, and plastic deformation of Li metal. The study begins with a revisit of the deformation-mechanism map for Li metal under a wide range of temperatures, stress, and deformation rates. This map serves as the basis for the mechanical characterization in the phase-field model. The large inelastic deformation of Li is considered by introducing an advection term into the Allen-Cahn equation, which is used to describe the dynamic evolution of the Li and void phases. The effects of current density and stack pressure on void evolution and Li penetration are studied based on the model predictions. By combining the simulation results with the experimental data from publications, we obtain the stable operation zone of stack pressure and applied current density. In this zone, the Li/SE interface can enable stable stripping and plating of Li metal. The same phase-field modeling framework is transferred to investigate the Li-Mg alloy/SE interface considering Li-Mg alloy is also used as the anode. The fundamental difference between Li/SE and Li-Mg/SE is analyzed accordingly. This study provides a useful tool for the design, manufacturing, and management of next-generation batteries by providing important scientific insights into the electro-chemo-mechanical processes of different anode materials under various operational conditions.

High-conductivity and elasticity interface consisting of Li-Mg alloy and Li3N on silicon for robust Li-ion storage

Silicon (Si) materials are one of the industry's preferred choices for lithium-ion batteries (LIBs) anode in the near and mid-term due to their high theoretical capacity, abundance in earth and safety. However, the weak and low conductivity of the solid electrolyte interface (SEI) leads to poor cycling stability, limited Coulombic efficiency, and poor rate performance, consequently hampering practical applications. Herein, the MgSiN2 functional coating is prepared by in-situ evolution of Mg2Si on porous micro-Si (pMSi@MgSiN2) via a scalable one-step low-temperature nitriding strategy. Interestingly, MgSiN2 is converted into the robust multi-functional interface composed of highly conductive Li3N and elastic Li-Mg alloy during subsequent lithium intercalation, which is studied by in-situ/ex-situ methods. The multi-functional interface takes over the role of improving interfacial stability and ionic/electronic conductivity. As expected, the pMSi@MgSiN2 anode shows a high gravimetric capacity of 1981.5 mAh g−1 at 1.0 A g−1 after 150 cycles, together with a high initial Coulombic efficiency of over 88.4 %. Furthermore, a consider capacity of 894 mAh g−1 can be retained after 500 cycles at 5.0 A g−1. The results and strategy reveal a new route for the integrated design of Si interface or other alloy-type anode materials to the fast lithium storage performance.

Enhancing air stability of LiMg alloy anode through Yb segregation at grain boundaries

Owing to the ultrahigh theoretical specific capacity and the most negative electrochemical potential, lithium metal has become the most promising lithium battery anode material. However, it is highly susceptible to oxidation during industrial production and storage processes. The polycrystal surface of the lithium metal anode serves as the site for oxidation reaction, and the reaction pathway is inevitably influenced by the microstructure of the anode surface. especially the grain boundaries, which with higher activity than a crystallographic plane, leading to intercrystalline oxidation reactions. Within the LiMg@Yb alloy system, ytterbium (Yb) segregated at the grain boundaries, leading to a reduction in intercrystalline energy as predicted by Density Functional Theory (DFT) calculations. Thus, the LiMg@Yb alloy can effectively suppress intercrystalline oxidation reactions and enhance air stability. More impressively, even exposed to ambient air for 0.5 h, the LiMg@Yb-0.5||LFP full cell exhibited a higher capacity retention rate (80.7%) than the bare Li-0.5||LFP (35.9%) after 100 cycles. This work presents a new approach for enhancing air stability by inhibiting intercrystalline oxidation reactions between anodes and air.

Operando Characterization of Plating and Stripping Dynamics of Li-Mg Alloy Anode and Sulfide Solid Electrolyte Interface

All-solid-state lithium metal batteries are projected to offer one of the highest specific energy among rechargeable batteries, positioning them as a front-runner for electric vehicle applications. Lithium metal anodes outperform conventional graphite anodes in terms of cell-level energy density. However, maintaining a conformal metal–electrolyte contact is a great challenge. The volumetric change of the lithium metal anode during stripping produces voids, which deteriorates the Li–electrolyte contact. To address this challenge, β-phase Li solid solution (i.e., Li-Mg alloy) has been shown to exhibit improved contact with the solid electrolyte during stripping. Moreover, Li solid solution has a similar electrochemical potential as Li, making it a potential replacement for Li metal anodes without sacrificing cell-level energy density. In this study, we show that the chemical properties of the alloy play an essential role in the morphological stability of metal–solid electrolyte interface. We compare the stripping behavior of pure Li and Li-Mg alloy anodes in argyrodite electrolyte and characterize the morphological evolution of the interface using operando scanning electron microscopy (SEM). We also analyze the electro-chemo-mechanical properties of Li and Li alloy anodes during stripping with galvanostatic electrochemical impedance spectroscopy (GEIS) to compare the influence of composition change and interfacial void on the electrode overpotential and interface resistance. Our research visualizes the morphological and compositional evolution of alloy metal anode during stripping and rationalizes their improved interfacial stability against solid electrolytes.Acknowledgment: This work was supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Vehicle Technologies Program under Contract DE-EE0008864. Figure 1

Stack Pressure Dependence of Li Stripping/Plating Performance in All-Solid-State Li Metal Cells Containing Sulfide Glass Electrolytes.

Sulfide-based all-solid-state Li/S batteries have attracted considerable attention as next-generation batteries with high energy density. However, their practical applications are limited by short-circuiting due to Li dendrite growth. One of the possible reasons for this phenomenon is the contact failure caused by void formation at the Li/solid electrolyte interface during Li stripping. Herein, we studied the operating conditions, such as stack pressure, operating temperature, and electrode composition, that could potentially suppress the formation of voids. Furthermore, we investigated the effects of these operating conditions on the Li stripping/plating performance of all-solid-state Li symmetric cells containing glass sulfide electrolytes with a reduction tolerance. As a result, symmetric cells with Li-Mg alloy electrodes instead of Li metal electrodes exhibited high cycling stability at current densities above 2.0 mA cm-2, a temperature of 60 °C, and stack pressures of 3-10 MPa. In addition, an all-solid-state Li/S cell with a Li-Mg alloy negative electrode operated stably for 50 cycles at a current density of 2.0 mA cm-2, stack pressure of 5 MPa, and temperature of 60 °C, while its measured capacity was close to a theoretical value. The obtained results provide guidelines for the construction of all-solid-state Li/S batteries that can reversibly operate at high current densities.

An ultrastrong 3D architecture interface with fast and smooth Li-ion deposition for high-capacity Li metal anode

Lithium metal anode (LMA) is one of the most promising anodes for high-performance energy storage system in the future, which is limited by dendrite growth and volume expansion. Herein, a 3D lithium metal anode modification composed of nanodiamond particles coated by MgO and amorphous carbon is developed to balance the physical stability and Li-ion conductivity for large-capacity LMA. Diamond with high Young's modulus leads lateral growth of dendrites, while stacked particles disperse the local current density. Formed by displacement reaction, Li-Mg alloy renders diamond-based anode with rich ion transmission channels and high lithiophilicity, contributing to low nucleation overpotential. As a result, with large capacity of 10 mAh cm−2 at high current density of 5 mA cm−2, the composite anode can cycle stably for over 1200 h with small overpotential at about 30 mV.

Dimensionally Stable Composite Li Electrode with Cu Skeleton and Lithophilic Li-Mg Alloy Microstructure.

Lithium electrodes have gained increasing attention in recent years for their promising applications in high-energy-density secondary batteries. However, structural instability during cycling remains a considerable obstacle to development. In this study, a dimensionally stable Li-Mg/Cu composite electrode was fabricated. Cu foam as a plate grid can sustain the structure, and Li-Mg alloy as the active and lithophilic component can guide the uniform Li plating within the composite. Thus, Li-Mg/Cu electrode shows long-term stability in terms of dimensional change and surface morphology. This work provides a facile and practical way to fabricate composite Li electrodes with high dimensional stability for secondary batteries.

Versatile Asymmetric Separator with Dendrite-Free Alloy Anode Enables High-Performance Li-S Batteries.

Lithium–sulfur batteries (LSBs) with extremely‐high theoretical energy density (2600 Wh kg−1) are deemed to be the most likely energy storage system to be commercialized. However, the polysulfides shuttling and lithium (Li) metal anode failure in LSBs limit its further commercialization. Herein, a versatile asymmetric separator and a Li‐rich lithium–magnesium (Li–Mg) alloy anode are applied in LSBs. The asymmetric separator is consisted of lithiated‐sulfonated porous organic polymer (SPOP‐Li) and Li6.75La3Zr1.75Nb0.25O12 (LLZNO) layers toward the cathode and anode, respectively. SPOP‐Li serves as a polysulfides barrier and Li‐ion conductor, while the LLZNO functions as an “ion redistributor”. Combining with a stable Li–Mg alloy anode, the symmetric cell achieves 5300 h of Li stripping/plating and the modified LSBs exhibit a long lifespan with an ultralow fading rate of 0.03% per cycle for over 1000 cycles at 5 C. Impressively, even under a high‐sulfur‐loading (6.1 mg cm−2), an area capacity of 4.34 mAh cm−2 after 100 cycles can still be maintained, demonstrating high potential for practical application.

Dual-Conductive Li alloy composite anode constructed by a synergetic Conversion-Alloying reaction with LiMgPO4

With the increasing energy density demand for lithium-ion batteries, Li metal anode catches much attention owing to its ultrahigh theoretical capacity and low electrochemical potential. However, lithium is highly reactive and easily forms dendrites and fractures during deposition, which leads to low coulombic efficiency and severe safety problem. Thereby, suppressing the growth of Li dendrites to stabilize the Li/electrolyte interface is vital to lithium metal anode. Here, we introduce a strategy to construct a Li alloy/ion-conductor composite anode via a one-step conversion-alloying reaction. The pristine LiMgPO4 are converted to ion-conductive Li3PO4 and Mg, and Mg reacts with Li to form Li-Mg alloy, resulting in a final Li-LMP composite. The alloying and the generation of nanosized Li3PO4 not only enhance the mechanical strength of Li-LMP, making it more durable to the local stress during cycling, but also enhance ion transfer inside Li-LMP, showing a faster kinetic mass transfer process. As a consequence, Li-LMP shows promoted rate performance (LFP || Li-LMP could deliver 72 mAh g−1 at 10C) and cycle stability both in ether and carbonate electrolytes.

Research of Li-Mg Alloy Electrode for All Solid States Battery

All solid state Li metal battery is regarded as the promising next-generation energy storage device due to the high theoretical energy density and safety. However, the practical application of ASS Li-metal batteries is still limited owing to the cycle stability of both the cathode and lithium metal anode. In particular, the instability in the bulk and at the surface of the lithium anode during cycling becomes a huge obstacle for the practical application of ASS Li-metal batteries, based on the consideration of improving the stability in the bulk and at the surface of the lithium anode.Our experimental results reveal that the robust passivation layer is formed on the surface of the Li-Mg alloy anode, which is helpful to reduce side reactions, and enable the smooth surface morphology of anode during cycling.Meanwhile, the mixed electron and Li-ion conducting matrix of the Li-poor Li-Mg alloy as a porous skeleton structure can also be formed after delithiation, which can guarantee the structural integrity of the anode in the bulk during Li stripping and plating step. Therefore, the Li-rich Li-Mg alloy is demonstrated to be a very promising anode material for ASS Li-metal battery.

3D Printing Lithium Salt towards Dendrite-free Lithium Anodes

Three-dimensional (3D) printing is being progressively utilized to construct various customized architectures for batteries and supercapacitors. Here, 3D printing lithium salt (lithium fluoride, LiF) is developed to construct chemically stable and electrochemically friendly salt scaffolds based on a printable LiF colloidal gel. Owing to the high porosity of LiF scaffolds, lithium-magnesium alloy (Li-Mg) can be facilely infused into the 3D scaffolds towards Li anodes. In the resultant Li anodes, 3D printed LiF scaffolds not only enable to preserve well the integrity of the whole electrodes, but also facilitate the formation of uniform LiF-rich solid electrolyte interphase (SEI) layers, significantly enhancing Li+ diffusion rates at Li anode/electrolyte interface; Li-Mg alloy plays a crucial role to promote the uniform nucleation and growth of Li. Consequently, a dendrite-free lithium anode is achieved with an ultralong cycling time of 2000 h, a low overpotential of 18 mV, and good deep Li stripping and plating properties.

An Electron/Ion Dual-Conductive Alloy Framework for High-Rate and High-Capacity Solid-State Lithium-Metal Batteries.

The solid-state Li battery is a promising energy-storage system that is both safe and features a high energy density. A main obstacle to its application is the poor interface contact between the solid electrodes and the ceramic electrolyte. Surface treatment methods have been proposed to improve the interface of the ceramic electrolytes, but they are generally limited to low-capacity or short-term cycling. Herein, an electron/ion dual-conductive solid framework is proposed by partially dealloying the Li-Mg alloy anode on a garnet-type solid-state electrolyte. The Li-Mg alloy framework serves as a solid electron/ion dual-conductive Li host during cell cycling, in which the Li metal can cycle as a Li-rich or Li-deficient alloy anode, free from interface deterioration or volume collapse. Thus, the capacity, current density, and cycle life of the solid Li anode are improved. The cycle capability of this solid anode is demonstrated by cycling for 500 h at 1 mA cm-2 , followed by another 500 h at 2 mA cm-2 without short-circuiting, realizing a record high cumulative capacity of 750 mA h cm-2 for garnet-type all-solid-state Li batteries. This alloy framework with electron/ion dual-conductive pathways creates the possibility to realize high-energy solid-state Li batteries with extended lifespans.

Transient Behavior of the Metal Interface in Lithium Metal-Garnet Batteries.

The interface between solid electrolytes and Li metal is a primary issue for solid-state batteries. Introducing a metal interlayer to conformally coat solid electrolytes can improve the interface wettability of Li metal and reduce the interfacial resistance, but the mechanism of the metal interlayer is unknown. In this work, we used magnesium (Mg) as a model to investigate the effect of a metal coating on the interfacial resistance of a solid electrolyte and Li metal anode. The Li-Mg alloy has low overpotential, leading to a lower interfacial resistance. Our motivation is to understand how the metal interlayer behaves at the interface to promote increased Li-metal wettability of the solid electrolyte surface and reduce interfacial resistance. Surprisingly, we found that the metal coating dissolved in the molten piece of Li and diffused into the bulk Li metal, leading to a small and stable interfacial resistance between the garnet solid electrolyte and the Li metal. We also found that the interfacial resistance did not change with increase in the thickness of the metal coating (5, 10, and 100 nm), due to the transient behavior of the metal interface layer.

Electro-optical performance of inorganic monolithic electrochromic device with a pulsed DC sputtered Li x Mg y N ion conductor

Lithium magnesium nitride (Li x Mg y N) thin films were deposited by pulsed DC reactive magnetron sputtering from a LiMg alloy target in the mixture gas of Ar and N2. The as-prepared Li x Mg y N films were amorphous. A monolithic inorganic electrochromic device (ECD) based on WO3/NiO complementary structure was fabricated using the Li x Mg y N as the ion conductor layer. The addition of a 150-nm thick Si3N4 buffer layer between Li x Mg y N and NiO made coloration and bleaching reversible and stable. Electrochemical and optical characterizations were conducted to evaluate the performance of the ECD. Electro-optical data were recorded for both 1000 chronoamperometric cycles and 1000 voltammetric cycles. Activation and degradation of the electro-optical properties of the ECD were observed.

The Nature of Electrochemical Delithiation of Li-Mg Alloy Electrodes: Neutron Computed Tomography and Analytical Modeling of Li Diffusion and Delithiation Phenomenon

Li-Mg alloys are promising as positive electrodes (anodes) for Li-ion batteries due to the high Li storage capacity and the relatively lower volume change during the lithiation/delithiation process. They also present a unique opportunity to image the Li distribution through the electrode thickness at various delithiation states. In this work, spatial distributions of Li in electrochemically delithiated Li-Mg alloy electrodes have been quantitatively determined using neutron tomography. Specifically, the Li concentration profiles along thickness direction are determined. A rigorous analytical model to quantify the diffusion-controlled delithiation, accompanied by phase transition and boundary movement, has also been developed to explain the delithiation mechanism. The analytical modeling scheme successfully predicted the Li concentration profiles which agreed well with the experimental data. It is demonstrated that during discharge Li is removed by diffusion through the solid solution Li-Mg phases and this proceeds with β→α phase transition and the associated phase boundary movement through the thickness of the electrode. This is also accompanied by electrode thinning due to the change in molar volume during delithiation. Following the approaches developed here, one can develop a rigorous and quantitative understanding of electrochemical delithiation in electrodes of electrochemical cells, similar to that in the present Li-Mg electrodes.

The Crystal Structure and Mechanical Property of AZ80-2%Li Mg Alloy

In this study, the crystal structure and mechanical property of AZ80-2%Li Mg alloy are investigated. Experimental results show that the density of AZ80 Mg alloy can be reduced to be 1.71 g/cm3 by addition of 2wt% Li. The as-extruded AZ80-2%Li Mg alloy exhibits a two-phase microstructure of α and β phases, with fine strips along the extrusion direction. The fracture strain increases significantly with increasing deformation temperature, and the tensile strengths hardly change at below 100oC. The tensile strength increases, but fracture strain decreases, with increasing strain rate. The 400°C solid-solution treated AZ80-2%Li Mg alloy will produce the AlLi precipitate after aging at 170°C, and produce the Mg17Al12 precipitate after aging at 250°C. The AZ80-2%Li Mg alloy with aging at both 170°C and 250°C will exhibit the phenomenon of precipitation hardening.

A new dehydrogenation mechanism for reversible multicomponent borohydride systems—The role of Li–Mg alloys

A new dehydrogenation mechanism for LiBH4-MgH2 mixtures revealed that magnesium destabilised the LiBH(4) resulting in complete dehydrogenation of the borohydride phase and the formation of a Li-Mg alloy.

Growth and band gap of the filled tetrahedral semiconductor LiMgN

The cubic AlN-like compound, LiMgN, can be considered as a zinc blende-like (MgN) − lattice partially filled with He-like Li + interstitials. LiMgN was synthesized by direct reaction between N 2 and LiMg alloy at around 800°C for 8 h. Polycrystalline crystals are grown as cornflake-like shapes with a light yellow color and show the LiMgN-phase (the lattice constant a=4.955±0.005 Å) except for non-reactant LiMg and oxide (LiNO 3). The ordered structure between Li and Mg is not confirmed exactly by X-ray diffraction studies. The band gap of as-grown crystals evaluated using photoacoustic spectroscopy is 3.2 eV, which value is supported by an optical transmission spectrum. The band gap value of LiMgN is close to that of GaN (zinc blende, E g=3.45 eV).