Low Migration Energy Barrier Research Articles

Reasonable construction of low migration energy barrier and continuous proton transfer channels via bimetallic MOFs nanofibers (MIL-(Cr Al)–NH2) for its composite proton exchange membrane

Reasonable construction of low migration energy barrier and continuous proton transfer channel is the key to improving the performance of composite proton exchange membranes. In this paper, we prepared a novel bimetallic MOFs (MIL-(Cr Al)–NH2) nanofibers (MCANs) consisting of Cr and Al elements by electro-blown spinning method (EBS) and hydrothermal synthesis, and subsequently introduced them into non-fluorinated sulfonic acid polymer sulfonated polysulfone (SPSF) matrix to obtain composite proton exchange membranes (MCANs@SPSF). Importantly, MCANs successfully constructed relatively long-range continuous unsaturated metal site proton transfer channels provided by the Cr-based MOFs, thereby reducing the proton migration energy barrier in the MCANs@SPSF, which confirmed by the density functional theory (DFT) calculation. In detail, DFT studies indicated that the migration energy barrier between H+ and MCANs was 1.677 eV, while that of single Al-based MOF (MAN) and single Cr-based MOF (MCN) were 1.879 eV and 1.762 eV respectively. The existence of efficient low migration energy barrier and continuous proton transfer channels made the proton conduction efficiency of MCANs@SPSF greatly improved, that was under the condition of 80 °C and 100 % RH, the proton conductivity of MCANs@SPSF reached the maximum value of 0.358 S cm−1 and the power density reached 104 mW cm−2. Moreover, MCANs@SPSF-5 displayed best DMFC durability performance with only 14.65 % voltage loss under 24h test. In addition, due to the acid-base pair interaction between MCANs and SPSF enhanced the interface binding force between the two phases, meanwhile, the pore structure of MOFs also had a certain adsorption effect on methanol, thus reducing the methanol permeability, and the addition of 5 wt% MCANs in SPSF was tested to reduce the methanol permeability to 5.53 × 10-7 cm2 s−1. Overall, this work provided a new strategy for construction of low migration energy barrier and continuous proton transfer channels, which was beneficial for the development of high performance proton exchange membranes.

Robust and Adhesive Laminar Solid Electrolyte with Homogenous and Fast Li-Ion Conduction for High-Performance All-Solid-State Lithium Metal Battery.

Constructing composite solid electrolytes (CSEs) integrating the merits of inorganic and organic components is a promising approach to developing high-performance all-solid-state lithium metal batteries (ASSLMBs). CSEs are now capable of achieving homogeneous and fast Li-ion flux, but how to escape the trade-off between mechanical modulus and adhesion is still a challenge. Herein, a strategy to address this issue is proposed, that is, intercalating highly conductive, homogeneous, and viscous-fluid ionic conductors into robust coordination laminar framework to construct laminar solid electrolyte with homogeneous and fast Li-ion conduction (LSE-HFC). A 9µm-thick LSH-HFC, in which poly(ethylene oxide)/succinonitrile is adsorbed by coordination laminar framework with metal-organic framework nanosheets as building blocks, is used here as an example to determine the validity. The Li-ion transfer mechanism is verified and works across the entire LSE-HFC, which facilitates homogeneous Li-ion flux and low migration energy barriers, endowing LSE-HFC with high ionic conductivity of 5.62×10-4Scm-1 and Li-ion transference number of 0.78 at 25°C. Combining the outstanding mechanical strength against punctures and the enhanced adhesion force with electrodes, LSE-HFC harvests uniform Li plating/stripping behavior. These enable the realization of high-energy-density ASSLMBs with excellent cycling stability when being assembled as LiFePO4/Li and LiNi0.6Mn0.2Co0.2O2/Li cells.

Na2.5Cr0.5Zr0.5Cl6: A New Halide-Based Fast Sodium-Ion Conductor.

All-solid-state batteries employing solid electrolytes (SEs) have received widespread attention due to their high safety. Recently, lithium halides are intensively investigated as promising SEs while their sodium counterparts are less studied. Herein, a new sodium-ion conductor with a chemical formula of Na2.5Cr0.5Zr0.5Cl6 is reported, which exhibits high room temperature ionic conductivity of 0.1 mScm-1 with low migration energy barrier of ≈0.41eV. Na2.5Cr0.5Zr0.5Cl6 has a Fm-3m structure with 41.67mol.% of cationic vacancies owing to the occupation of Cr (8.33mol.%) and Zr (8.33mol.%) ions at Na sites. Supercell calculations show that the lowest columbic energy configuration has Cr/Zr/V (where V is the vacancy) clusters in the structure. Nonetheless, the clusters have mixed effects on the sodium ion conduction pathway, based on the Bond Valence Energy Landscape calculation. A global 3D Na-ion transport percolation network can be revealed in the lowest energy supercell. Effective pathways are connected through the NaCl6 and VCl6 nodes. Besides, Raman spectroscopy and 23Na solid-state nuclear magnetic resonance spectroscopy further prove the tunable structure of the SEs with different Cr to Zr ratios. The optimization between the concentration of Na+ and vacancies is crucial to create an improved network of Na+ diffusion channels.

First-row transition metal carbide nanosheets as high-performance cathode materials for lithium-sulfur batteries.

Despite the prodigious potential of lithium-sulfur (Li-S) batteries as future rechargeable electrochemical systems, their commercial implementation is hindered by several vital issues, including the shuttle effect and sluggish migration of lithium-polysulfides leading to rapid capacity fading. Here, we systematically investigate the potential of first-row two-dimensional transition metal carbides (TMCs) as sulfur cathodes for Li-S batteries. The adsorption strength of lithium-polysulfides on TMCs is induced by the amount of charge transfer from the former to the latter and the proposed periodic relationship between sulfur in Li2S and 3d-transition metals. Our findings show that the VC nanosheet possesses immense anchoring potential and exhibits a comparatively low migration energy barrier for lithium-ion and Li2S molecules. Additionally, we report ab initio molecular dynamics simulations for lithiated polysulfide species anchored on a TMC-based model with a liquid-electrolyte medium. The microscopic reaction mechanism, revealed by the evolution of the reaction voltage during lithiation, demonstrates that the dissolution of high-order lithium-polysulfides in the electrolytes can be prevented due to their robust interaction with TMC-based cathode materials. These appealing features suggest that TMCs present colossal performance improvements for anchoring lithium-polysulfides, stimulating the active design of sulfur cathodes for practical Li-S batteries.

Theoretical studies of C3N3Li/graphene heterostructure as a promising anode material of lithium-ion battery

The electrochemical properties of g-CN and g-CN/graphene heterostructure as anode materials for lithium-ion batteries were investigated by density functional calculations. It is shown that the Li adsorbed in the pore of g-CN has strong interactions with g-CN and a high diffusion energy barrier, leading to Li being trapped in the pores. After the pores of g-CN are fully adsorbed (C3N3Li), the migration energy barrier of Li ion on the surface of C3N3Li decreased to 0.56 eV. The calculated capacity (197 mAh/g) using C3N3Li as the host system is in agreement with experiment results. Similarly, the adsorption energy of Li in the pore of g-CN in the g-CN/graphene heterostructure is − 2.74 eV and the diffusion energy barrier (2.44 eV) for Li ion is still too high to migrate in the adjacent pores. Therefore, C3N3Li/graphene was used as the host anode system, and suitable adsorption energies (−0.81 eV), low migration energy barrier (0.43 eV), and a capacity of 694 mAh/g were obtained, which suggests that C3N3Li/graphene can be a promising anode material for Li-ion battery.

Revealing the Valence Evolution of Metal Element in Heterostructures for Ultra‐High Power Li‐Ion Capacitors

AbstractThe difficulty in matching cathode and anode kinetics due to slow ion transport in anodes constrains the development of lithium‐ion capacitors. Heterogeneous structures with built‐in electric field can promote lithium‐ion migration and improve the anode reaction kinetics. However, the valence evolution of metal elements in heterostructures during charging/discharging processes is often overlooked. Inspired by theoretical calculations, transition metal selenides heterostructures (FeSe2/CoSe2) with low migration energy barriers (E b = 0.35 eV) are successfully engineered and fabricated. As expected, the designed heterostructure material exhibits outstanding rate performance (512 mAh g−1 at 30 A g−1) and ultra‐high pseudocapacitance contribution (98.02% at 1.0 mV s−1), exceeding the state‐of‐the‐art values for anodes. Impressively, synchrotron X‐ray absorption spectroscopy (SXAS) and ex situ XPS find that the valence states of the Fe and Co elements in the heterogeneous structure gradually increase as charging and discharging proceeds, inducing a continuous climb in reversible specific capacity, while further reducing the migration energy barrier in the heterogeneous structure (E b = 0.20 eV). This work reveals that the valence states of iron and cobalt elements increase as charging and discharging proceeds, providing theoretical guidance for improving the anode kinetics and revealing the capacity rise mechanism of other transition metal compounds.

Performances of O- and S-functionalized Mo2C monolayer in lithium ion batteries: Theoretical and experimental research

MXenes exhibit outstanding potential as electrode materials for lithium-ion batteries (LIBs) due to their extensive specific surface area, superior electrical conductivity and abundant surface-active terminations. The electrochemical properties of Mo2CT2 (T = bare, -O, -S) as anodes for LIBs have been studied by adopting the first-principles calculations and experiments. The results reveal that Mo2CO2 has a negative impact on Li storage, leading to a slight decrease in theoretical capacity and a significant increase in average voltage. The low migration energy barriers of Mo2C, Mo2CO2 and Mo2CS2 are estimated as 0.037 eV, 0.145 eV and 0.244 eV. Moreover, the predicted average voltages of Mo2C and Mo2CS2 are 0.79 V and 0.11 V, rendering them highly desirable for low charging voltage applications. It is striking that the storage capacity of Mo2C is improved remarkably from 263 mA·h/g to 400 mA·h/g by introducing S functional group. Herein, experimental batteries are fabricated with Mo2CSx and Mo2C as anodes to investigate their electrochemical properties, which exhibit both stability and reversibility. Interestingly, the exceptional discharge capacity and cycling stability of Mo2CSx can be attributed to its unique structure, which is consistent with the calculated results. Therefore, S-decorated Mo2C is a more suitable anode for LIBs with excellent performance, which also provides guidance for introducing appropriate functional groups to enhance the electrode performance of other MXenes.

Three-dimensional flower spheres MoSe2/NiSe heterostructure with fast kinetic and stable structure for durable sodium-ion storage

Due to the large size of Na+ and the slow redox kinetics, the energy storage performance of sodium ion batteries (SIBs) is far from satisfactory. Heterojunction with layered structure has great potential in advanced material of SIBs. Herein, the 3D flower spheres MoSe2/NiSe heterostructure with fast dynamic properties was proposed, which shows enhancement in the adsorption and storage capacity of Na+ with a low migration energy barrier. Unique structure design can further effectively alleviate the volume expansion during sodiation/desodiation process. Furthermore, the DFT calculation results reveal the charge transfer mechanism between NiSe and MoSe2, as well as improved intrinsic electric structure of MoSe2/NiSe. In consequence, the designed MoSe2/NiSe possesses a good cyclability over 3000 cycles with a capacity of 172 mAh/g at 5.0 A/g, and the full cell with Na3V2(PO4)3/C cathode shows high-rate performance of 276 mAh/g at 2.0 A/g, which solidly proves the feasibility of the designed MoSe2/NiSe anode in the practical application. This work shows that the heterojunction can achieve long-lasting sodium electrochemistry and expand to other energy storage fields.

Promising anode materials for alkali metal ion batteries: a case study on cobalt anti-MXenes.

There is continuous demand for energy storage devices with high energy densities in consumer electronics, electric vehicles, and the grid energy market. Although commercial lithium-ion batteries (LIBs) satisfy the current needs, the limited availability of their raw materials and the moderate specific charge capacities (SCCs) of LIBS have motivated scientists to search for alternate anode materials for LIBs and create technologies beyond LIBs. In this work, we studied the potential of six cobalt anti-MXenes (CoAs, CoB, CoP, CoS, CoSe, and CoSi), a class of newly discovered 2D materials, as anode materials for lithium, sodium, and potassium ion batteries (LIBs, NIBs, and KIBs). We found that these materials are good electrical conductors and have high adsorption stability for alkali metal ions, which helps to prevent the formation of dendrites and increase the cycle life of the battery. They also show moderate to low migration energy barriers (MEBs), indicating the potential for faster charge-discharge kinetics. We also explain the slightly counter-intuitive result of observing low MEBs along with high adsorption stability. Furthermore, Co-anti-MXenes can adsorb multiple alkali atoms per formula unit, resulting in high specific charge capacities and low average anodic voltages. For example, as anode materials for lithium-ion batteries, CoP and CoSi have SCC values of 1075.4 mA h g-1 and 934 mA h g-1, and anodic voltages as low as 0.28 V and 0.43 V, respectively. Moreover, even the maximally metalated Co-anti-MXenes did not show agglomeration tendency at room temperature. Furthermore, the volume expansion of these materials is minimum for both Li and Na adsorption. As a whole, we find that Co-anti-MXenes are promising as anode materials for alkali metal ion batteries.

A novel phase of superionic conductor β'-Na3PS4 with a large band gap and a low migration barrier.

Na3PS4 crystals with high ionic conductivity are promising solid-state electrolytes. Here, a novel phase of Na3PS4 (β'-NPS) crystallizing in a cubic lattice with a space group of P4̄3m was systematically investigated using first-principles calculations. First of all, β'-NPS is determined to be thermodynamically, dynamically and mechanically stable. The phase transition from tetragonal Na3PS4(α-NPS) to a cubic β'-NPS system occurs at approximately 480 K, suggesting high feasibility of experimental access. Moreover, the β'-NPS is an insulator with a large band gap of 4.05 eV and a low migration energy barrier of 0.10 eV for an interstitial Na ion. Significantly, a novel Na ion diffusion mechanism, that is, interstitial diffusion, is proposed, in contrast to traditional vacancy diffusion or kick-off diffusion as observed in most solid electrolytes. This work proposes β'-NPS as a promising superionic conductor for sodium ion batteries and provides theoretical guidance towards designing future ideal solid-state electrolytes.

Regulation of 3d‐Transition Metal Interlayered Disorder by Appropriate Lithium Depletion for Li‐Rich Layered Oxide with Remarkably Enhanced Initial Coulombic Efficiency and Stability

AbstractLi‐rich materials are among the most promising cathode materials for lithium‐ion batteries thanks to their high specific capacity. However, they exhibit poor structural stability, resulting in low initial Coulombic efficiency and limited cycle stability. Herein, a long‐neglected Li‐deficient state is realized for a Co‐free lithium‐rich cathode through a facile calcination medium‐induced surface‐corrosion (CMISC) strategy for alleviating the aforementioned drawbacks. The as‐constructed Li‐deficient lithium‐rich cathode of Li1.2‐σMn0.6Ni0.2O2 (d‐LMNO) exhibits an enhanced capacity of 272 mAh g−1, improved initial efficiency of 84.5%, and cycle stability with 82.0% retention over 200 cycles. In addition, multiple in situ and ex situ investigations confirm the appropriate lithium depletion regulated 3d‐transition metal interlayered disorder, resulting in excellent structural reversibility of d‐LMNO. Also, theory simulations suggest that the crystal structure with Li‐defects has lower energy and Li‐diffusion energy barrier when the coordination interlayer 3d‐metal has more Ni closer to the diffused Li, meaning less interlayered disorder. And the migration of Li close to the vacancy is dominated by a tetrahedral site hopping path in the presence of additional vacancies around the Li vacancy, which has a low migration energy barrier. Moreover, similar results achieved in Co‐containing Li‐rich cathodes further demonstrate the universality of this simple CMISC strategy, exhibiting great potential for performance improvement and applicability.

Theoretical insight into lithium triborates as solid-state electrolytes

Owing to the inherent properties combining high ionic conductivity and electrochemical stability, the lithium triborates (LBOs) have emerged as a promising solid-state electrolyte for next-generation batteries. Specific fundamental details of the ionic conduction mechanism and related physicochemical properties remain to be understood. In this study, using the first-principles density functional theory calculations, we present a systematic computational investigation on LBOs in the respect of electronic structures, mechanical and thermodynamic properties, Li-ion transport, and interfacial (with Li metal) behaviors. Our results show that LBO is a thermodynamically and mechanically stable insulator with an indirect wide bandgap of 6.4 eV. Notably, LBOs could behave as a fast Li-ion conductor with a low migration energy barrier (15 meV) and are characterized by a zig–zag Li+-diffusion path along the c direction. We found that the interface between Li metal and LBO is both physically and chemically stable with no new phase formed while exhibiting a metallic character due to the charge transfer from a Li metal. Our study highlights the intriguing promise of LBOs as solid-state electrolytes for high-energy cells.

Low‐strain TiP2O7 with three‐dimensional ion channels as long‐life and high‐rate anode material for Mg‐ion batteries

AbstractRechargeable magnesium batteries are identified as a promising next‐generation energy storage system, but their development is hindered by the anode−electrolyte−cathode incompatibilities and passivation of magnesium metal anode. To avoid or alleviate these problems, the exploitation of alternative anode materials is a promising choice. Herein, we present titanium pyrophosphate (TiP2O7) as anode materials for magnesium‐ion batteries (MIBs) and investigate the effect of the crystal phase on its magnesium storage performance. Compared with the metastable layered TiP2O7, the thermodynamically stable cubic TiP2O7 displays a better rate capability of 72 mAh g−1 at 5000 mA g−1. Moreover, cubic TiP2O7 exhibits excellent cycling stability with the capacity of 60 mAh g−1 after 5000 cycles at 1000 mA g−1, which are better than previously reported Ti‐based anode materials for MIBs. In situ X‐ray diffraction technology confirms the single‐phase magnesium‐ion intercalation/deintercalation reaction mechanism of cubic TiP2O7 with a low volume change of 3.2%. In addition, the density functional theory calculation results demonstrate that three‐dimensional magnesium‐ion diffusion can be allowed in cubic TiP2O7 with a low migration energy barrier of 0.62 eV. Our work demonstrates the promise of TiP2O7 as high‐rate and long‐life anode materials for MIBs and may pave the way for further development of MIBs.

O3-Type Na2/3Ni1/3Ti2/3O2 Layered Oxide as a Stable and High-Rate Anode Material for Sodium Storage

Sodium-ion batteries (SIBs) are currently the most promising candidates for large-scale energy storage devices owing to their low cost and abundant resources. Titanium-based layered oxides have attracted widespread attention as promising anode materials due to delivering a safe potential of about 0.7 V (vs Na+/Na) and a small volume contraction during cycles; P2-type Ti-based layered oxides are typically reported, due to the challenging synthesis of the O3-type counterpart resulting from the high percentage of unstable Ti3+. Herein, we report an anomalous O3-Na2/3Ni1/3Ti2/3O2 layered oxide as an ultrastable and high-rate anode material for SIBs. The anode material delivers a reversible capacity of 112 mA h g-1 after 300 cycles at 0.1 C, a good capacity retention rate of 91% after 1400 cycles at 2 C, and, in particular, a capacity of 52 mA h g-1 even at a high rate of 20 C (1780 mA g-1). Furthermore, the in situ X-ray diffraction monitoring reveals no phase transitions and almost zero strain both underlie the good long-cycle stability. The measured high apparent Na+ diffusion coefficient (2.06 × 10-10 cm2 s-1) and the low migration energy barrier (0.59 eV) from density functional theory calculations are responsible for the superior rate capability. Our results promise advanced high-performance O3-type Ti-based layered oxides as promising anode materials toward application for SIBs.

A highly efficient and informative method to identify ion transport networks in fast ion conductors

High-throughput analysis of the ion transport pathways is critical for screening fast ion conductors. Currently, empirical methods, such as the geometric analysis and bond valence site energy (BVSE) methods, are respectively used for the task. Geometric analysis method can only extract geometric and topological pathway properties without considering the interatomic interactions, while the BVSE method alone does not yield a geometric classification of the sites and interstices forming the pathway. Herein, we propose a highly efficient and informative method to identify interstices and connecting segments constructing an ion transport network by combining topological pathway network and BVSE landscape, which enables to obtain both the geometry and energy profiles of nonequivalent ion transport pathways between adjacent lattice sites. These pathways can be further used as the input for first-principles nudged elastic band calculations with automatically generated chains of images. By performing high-throughput screening of 48,321 Li-, Na-, Mg- and Al-containing ionic compounds from the Inorganic Crystal Structure Database based on the filter combining geometric analysis and BVSE methods, we obtain 1,270 compounds with connected ionic migration pathways of suitable sizes and low migration energy barriers, which include both previously reported fast ion conductors, and new promising materials to be explored further.

Highly Stable Two-Dimensional Iron Monocarbide with Planar Hypercoordinate Moiety and Superior Li-Ion Storage Performance.

Stable planar hypercoordinate motifs have been recently demonstrated in two-dimensional (2D) confinement systems, while perfectly planar hypercoordinate motifs in 2D carbon-transition metal systems are rarely reported. Here, by using comprehensive ab initio computations, we discover two new iron monocarbide (FeC) binary sheets stabilized at 2D confined space, labeled as tetragonal-FeC (t-FeC) and orthorhombic-FeC (o-FeC), which are energetically more favorable compared with the previously reported square and honeycomb lattices. The proposed t-FeC is the global minimum configuration in the 2D space, and each carbon atom is four-coordinated with four ambient iron atoms, considered as the quasi-planar tetragonal lattice. Strikingly, the o-FeC monolayer is an orthorhombic phase with a perfectly planar pentacoordinate carbon moiety and a planar seven-coordinate iron moiety. These monolayers are the first example of a simultaneously pentacoordinate carbon and planar seven-coordinate Fe-containing material. State-of-the-art theoretical calculations confirm that all these monolayers have significantly dynamic, mechanical, and thermal stabilities. Among these two monolayers, the t-FeC monolayer shows a higher theoretical capacity (395 mAh g-1) and can stably adsorb Li up to t-FeCLi4 (1579 mAh g-1). The low migration energy barrier is predicted as small as 0.26 eV for Li, which results in the fast diffusion of Li atoms on this monolayer, making it a promising candidate for lithium-ion battery material.

Lithium Chlorides and Bromides as Promising Solid‐State Chemistries for Fast Ion Conductors with Good Electrochemical Stability

AbstractEnabling all‐solid‐state Li‐ion batteries requires solid electrolytes with high Li ionic conductivity and good electrochemical stability. Following recent experimental reports of Li3YCl6 and Li3YBr6 as promising new solid electrolytes, we used first principles computation to investigate the Li‐ion diffusion, electrochemical stability, and interface stability of chloride and bromide materials and elucidated the origin of their high ionic conductivities and good electrochemical stabilities. Chloride and bromide chemistries intrinsically exhibit low migration energy barriers, wide electrochemical windows, and are not constrained to previous design principles for sulfide and oxide Li‐ion conductors, allowing for much greater freedom in structure, chemistry, composition, and Li sublattice for developing fast Li‐ion conductors. Our study highlights chloride and bromide chemistries as a promising new research direction for solid electrolytes with high ionic conductivity and good stability.

Lithium Chlorides and Bromides as Promising Solid-State Chemistries for Fast Ion Conductors with Good Electrochemical Stability.

Enabling all-solid-state Li-ion batteries requires solid electrolytes with high Li ionic conductivity and good electrochemical stability. Following recent experimental reports of Li3 YCl6 and Li3 YBr6 as promising new solid electrolytes, we used first principles computation to investigate the Li-ion diffusion, electrochemical stability, and interface stability of chloride and bromide materials and elucidated the origin of their high ionic conductivities and good electrochemical stabilities. Chloride and bromide chemistries intrinsically exhibit low migration energy barriers, wide electrochemical windows, and are not constrained to previous design principles for sulfide and oxide Li-ion conductors, allowing for much greater freedom in structure, chemistry, composition, and Li sublattice for developing fast Li-ion conductors. Our study highlights chloride and bromide chemistries as a promising new research direction for solid electrolytes with high ionic conductivity and good stability.

Theoretical study of lithium diffusion and fractionation in forsterite and its high-pressure phases

As a geochemical tracer in mantle studies, lithium isotopes play an important role in diffusion and fractionation in major mantle minerals. Olivine and its high-pressure phases, wadsleyite and ringwoodite, are considered to predominate in the upper mantle and transition zone on the earth. We carried out simulations of lithium isotopes’ diffusion and fractionation in Mg end member olivine and its high-pressure phases to learn the details of the signatures of lithium isotopes preserved in mantle materials. In this work, the diffusion and fractionation mechanisms between different lattice sites of lithium isotopes in forsterite (Mg2SiO4), wadsleyite (β-Mg2SiO4) and ringwoodite (γ-Mg2SiO4) at the atomic level are studied using empirical atomistic simulation techniques. It is found that Li can pass through the high-pressure phases (wadsleyite and ringwoodite) energetically much easier due to the low migration energy barriers via either substitutional or interstitial mechanism. The activation energy is high for Li diffusion along the interstitial path in the forsterite and decreases drastically with the assist of Mg vacancies. The temperature-dependent fractionation for two Li isotopes between two different lattice sites is calculated at the temperatures from 300 to 2500 K. This behavior generates the lighter Li storage in the near-surface mantle-derived rocks and provides insights into zoning and composition of lithium isotopes in olivine and its high-pressure phases.

Determination of Dynamically Stable Electrenes toward Ultrafast Charging Battery Applications

Electrenes, an atomically thin form of layered electrides, are very recent members of the 2D materials family. In this work, we employed first-principle calculations to determine stable, exfoliatable, and application-promising 2D electrene materials among possible M2X compounds, where M is a group II-A metal and X is a nonmetal element (C, N, P, As, and Sb). The promise of stable electrene compounds for battery applications is assessed via their exfoliation energy, adsorption properties, and migration energy barriers toward relevant Li, Na, K, and Ca atoms. Our calculations revealed five new stable electrene candidates in addition to previously known Ca2N and Sr2N. Among these seven dynamically stable electrenes, Ba2As, Ba2P, Ba2Sb, Ca2N, Sr2N, and Sr2P are found to be very promising for either K or Na ion batteries due to their extremely low migration energy barriers (5-16 meV), which roughly demonstrates 105 times higher mobility than graphene and two to four times higher mobility than other promising 2D materials such as MXene (Mo2C).