Bond Valence Energy Landscape Research Articles

Studies on highly stable Na7Fe3(P2O7)4 as anode materials for lithium-ion batteries and migration behavior of lithium ions

In this paper, Na7Fe3(P2O7)4 target material is firstly evaluated as potential anode material for lithium ion batteries. It is found to have good electro-chemical performance and high stability as anode material for lithium batteries. It shows a capacity of 290 mAh g−1 for 200 cycles and increases to 388 mAh g−1 for 1000 cycles at a current density of 150 mA g−1. The Coulomb efficiency is maintained at about 98 % during the long cycling. The ex-situ experimental results indicate that Na7Fe3(P2O7)4 has high structural stability and the changes of cell volume and cell parameters are <0.62 % during charging and discharging. The results of GITT data show that the diffusion coefficients range from 3.15 × 10−11 cm2 S−1 to 1.12 × 10−12 cm2 S−1.The Li+/Na+ diffusion paths are estimated by the Bond valence-energy landscape (BEL) method and the exact energy barriers and minimal energy paths (MEPs) are determined using the nudged elastic band (NEB) method implemented in density functional theories (DFT). A two dimensional Na+ diffusion network is observed and Na+ diffusion along c-axis is prohibited. For the initial discharge stage, Na+ migrates in the Na+ transportation channel with an energy barrier of 0.48 eV along a-axis and 0.46 eV along b-axis. For the discharge later on, the intercalated Li+ enters the nearby Na+ vacancies and also migrate in the Na+ channel except Li+ at 8f Lid sites, which will stay where it is firstly introduced because of the higher energy barrier of 0.75 eV. The immobility of Lid is one of the important reasons for the irreversible capacity loss after the initial charge/discharge cycle.

KTaCl6: High-voltage stable potassium-ion conducting chloride solid electrolyte

The exceptional electrochemical oxidative stabilities of halide solid electrolytes (SEs) have led to extensive research on Li and Na all-solid-state batteries. In this study, we report a new K+ SE, cubic KTaCl6, with a remarkable K+ conductivity of 1.0 × 10−5 S cm−1, synthesized via a mechanochemical method. This value represents a 1000-fold enhancement over that of samples prepared through heat treatment, which is remarkable among halide K+ SEs reported to date. Through structural characterization via X-ray diffraction, Rietveld analysis, and bond valence energy landscape calculations, we reveal three-dimensional K+ migration pathways facilitated by face-sharing KCl1211− cuboctahedra. This configuration is in contrast to that of the monoclinic KTaCl6 produced through annealing, which features discontinuous K+ migration pathways. These pathways are formed by the edge- or corner-sharing of KCl1211− anti-cuboctahedra, resulting in a significantly reduced K+ conductivity. Cyclic voltammetry measurements employing three-electrode cells indicate high electrochemical stability up to ≈3.7 V (vs. K/K+).

Exploring the Limits of Fe-Rich Chemistries in Na-Based CaFe2O4-Type Postspinel Oxides.

Structural trends, physical properties, and electrochemical performances of the NaFexRu2-xO4 system have been investigated. Synthesis attempts using both conventional solid-state routes and high-pressure methods were explored for the compositional range 1.0 ≤ x ≤ 1.67. Based on Rietveld refinements against powder X-ray diffraction data, analyses of 57Fe Mössbauer spectroscopy data, and elemental analysis by electron microprobe, the existence of a confined compositional solid solution (1 ≤ x ≤ 1.3) adopting the CaFe2O4-type postspinel structure is demonstrated. This is contrasted with the NaFexTi2-xO4 system, for which no evidence of a solid solution is observed. However, for all explored synthetic routes of NaFexRu2-xO4 compositions, a trivalent iron oxidation state is maintained. Structural analysis and qualitative bond valence energy landscape models reveal that the progressive integration of iron into the postspinel framework results in narrowed sodium ion diffusion channels, restricting electrochemical deintercalation of sodium. Consequently, the CaFe2O4-type iron-rich compounds explored in this study demonstrate limited potential as positive electrode materials for sodium batteries. It is expected that this fundamental insight will help guide the exploration of alternative NaM2O4-based positive electrode materials with similar structure types.

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.

Novel High-Temperature Modification of Belomarinaite KNaSO4: Crystal Structure and Thermal Order–Disorder Phase Transitions

Belomarinaite KNaSO4 (space group P3m1, a = 5.6072(3), c = 7.1781(4) Å and Z = 2) has been studied by high-temperature single crystal X-ray diffraction. The K and Na atoms are disordered, and M1(1c) and M2(1b) sites merge into an M1(2d)(K50%/Na50%) site with increasing temperature, and novel translationsgleiche phase transition of belomarinaite KNaSO4 (P3m1 → P-3m1) was revealed at 123 °C. Then, the temperature increase leads to phase transition of P3¯m1-polymorph of KNaSO4 to α-KNaSO4 (P63/mmc) at 446 °C, and sodium and potassium atoms in K1(1a) and Na1(1b) sites merged into an M4(2a)(K50%/Na50%) site. Crystal structures of KNaSO4 were refined at 300, 500 and 750 °C to R1 = 0.057, 0.056 and 0.048, respectively. The BVS maps and bond-valence energy landscape (BVEL) have been calculated, and the probability of the Na+ migration has been predicted using structural data for belomarinaite at 25 °C. The Na+ ion migration can occur at 2.14 eV in the ab plane and 2.80 eV along the c axis at 25 °C.

Li2GeS3: New Structural Type of Lithium Solid Electrolyte for All-Solid-State Batteries

Sulfide inorganic materials exhibit favorable qualities such as high ionic conductivity and mechanical softness, making them promising candidates for solid electrolytes in Li-ion all-solid-state batteries. Sulfide solid electrolytes exist in various structural types, including β-Li3PS4, Li10GeP2S12, argyrodite, Li4PS4I, Li7P3S11, and Li1.82SiP0.036S3. While these materials exhibit high ionic conductivities of up to ~10− 2 S cm− 1 at room temperature and possess mechanical softness, they also have limitations, such as a narrow electrochemical stability window and air instability, which can hinder their scalability. The electrochemical and air stabilities of a solid electrolyte (Li–M–S, where M = non-Li metal ions) are largely governed by its stability of crystal structure consisting of MSn polyhedra and Li ions. A material with a different crystal structure would show its distinct properties. However, despite extensive research, no single structure known to date has proven superior in all aspects of performance. Given the importance of crystal structure in developing high-performance solid electrolytes, exploring and identifying novel ion-conducting materials with unique crystal structures is imperative. Additionally, once a new structural type of material is discovered, its performance can be adjusted, enhanced, or optimized through various techniques, such as chemical substitution, morphology and particle size control, and surface coating. In this work, we discovered a new crystal structural type of Li-ion conductor Li2GeS3. It was first known in 2000 by Kanno et al., with only orthorhombic unit cell dimension reported. However, our study using ab initio structure determination techniques from powder X-ray diffraction data, similar to our previous works, unveiled its structure possessing a hexagonal P61 symmetry with lattice parameters of a = 6.80098(4) Å and c = 17.92827(11) Å, revealing a new type of crystal structure. Its structure is comprised of a distorted hexagonal close-packed arrangement of sulfur anions with three asymmetric metal atoms: Ge and Li2 are in tetrahedral cavities surrounded by sulfur atoms; Li1 is in the trigonal bipyramidal cavity. The material displayed an ionic conductivity of 1.63 × 10− 8 S cm− 1 at 303 K and 2.45 × 10− 7 S cm− 1 at 383 K. Bond valence energy landscape calculations revealed three-dimensional lithium diffusion pathways within the structure. These results suggest that Li2GeS3 is expected to be a host structure from which improved ionic conductors can be derived through appropriate chemical substitution.

Li2GeS3: Lithium Ionic Conductor with an Unprecedented Structural Type.

Lithium-ion batteries (LIBs) are widely used in electric vehicles, mobile electronic devices, and large-scale stationary energy storage systems. However, their liquid electrolytes present significant safety concerns due to their inherent flammability. To address this, the focus has shifted toward all-solid-state batteries (ASSBs) utilizing inorganic solid electrolytes that promise enhanced safety. In this work, we report the discovery of a new crystal structural type of Li-ion conductor, Li2GeS3, with a unique structure, synthesized by a solid-state reaction from Li2S and GeS2. It was first reported in 2000 with an orthorhombic unit cell, but its detailed crystal structure remains veiled. We have unveiled its structure for the first time, employing an ab initio structure determination technique from powder X-ray and time-of-flight neutron diffraction data. The compound has an unprecedented crystal structural type with a hexagonal P61 symmetry and a unit cell of a = 6.79364(4) Å and c = 17.90724(14) Å. Its structure is comprised of a distorted hexagonal close-packed arrangement of sulfur anions with three asymmetric metal atoms: Li1, Li2, and Ge are in tetrahedral cavities surrounded by sulfur atoms. The ionic conductivity of Li2GeS3 was measured to be 1.63 × 10-8 S cm-1 at 303 K and 2.45 × 10-7 S cm-1 at 383 K. Bond valence energy landscape calculations revealed three-dimensional lithium diffusion pathways within the structure. This novel crystal structure in Li2GeS3 holds the potential for developing high-performance ionic conductors through suitable chemical substitution and offers valuable insights into designing new ionic conductors for ASSBs.

The investigation of highly stable low strain orthorhombic Na2TiSiO5 as anode material for lithium ion batteries and the migration behavior of Na-Li ions

As a member of silicate anode materials, orthorhombic Na2TiSiO5, synthesized by solid state method, has excellent electrochemical properties and is a promising Lithium-ion battery anode material with long cycle stability and low strain. At a current density of 100 mA g−1, Na2TiSiO5 has a reversible capacity of 395.2 mA h g−1 after 200 cycles with Coulombic efficiencies more than 97%. A reversible capacity of 251.3 mA h g−1 after 1000 cycles is retained with Coulombic efficiencies more than 98%. ex-situ experiments show the high structural stability and a less than 0.67% change of unit cell parameters in the charge/discharge process. The bond valence energy landscape (BVEL) calculation reveals 12 voids, namely, 4c-1, 4c-2, 2b and 2a, in a unit cell. That corresponds to a nominal composition Na2Li(4c-1)Li(4c-2)Li0.5(2b)Li0.5(2a)TiSiO5 and a theoretical capacity of 398.1 mAh g−1. The ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations show that for both primitive orthorhombic Na2TiSiO5 and Li+ inserted Na2TiSiO5, Na+/Li+ are not active. However, with the insertion of 4C Li+, the occurrence of the synergic diffusion of Na+ and Ti4+ (4c Na+ -> 4c Ti4+ and 4c Ti4+ -> 2b vacancy) reliefs the extra strain, improves the structural stability during charge/discharge. The formation energy convex hull reveals 3 intermediate phases, that is Na2LiTiSiO5, Na2Li2TiSiO5 and Na2Li2.75TiSiO5, in the charge/discharge process.

NaAlCl4: New Halide Solid Electrolyte for 3 V Stable Cost-Effective All-Solid-State Na-Ion Batteries

Although high-voltage-stable halide solid electrolytes (SEs) have emerged, only a few Na+ halide SEs have been developed thus far. Moreover, the use of expensive elements reduces the suitability of all-solid-state Na-ion batteries (ASNBs). Herein, the new mechanochemically prepared orthorhombic NaAlCl4 is demonstrated to exhibit a 10-fold enhancement in Na+ conductivity (3.9 × 10–6 S cm–1 at 30 °C) compared to annealed samples. The feasibility of NaAlCl4 for ASNBs is also validated for the first time. X-ray Rietveld refinement with bond valence energy landscape calculations reveals 1D-preferable 2D Na+ conduction pathways. High-voltage stability up to ∼4.0 V (vs Na/Na+) is confirmed by electrochemical measurements and theoretical calculations. Furthermore, the outstanding electrochemical performance of NaCrO2/Na3Sn ASNBs at 30 and 60 °C is demonstrated (e.g., 82.9% capacity retention at the 500th cycle at 60 °C and 1C), shedding light on the potential of the cost-effective and safe energy storage systems.

Polymorphism and sodium-ion conductivity of NaTa2PO8 synthesized via the Li+/Na+ ion-exchange reaction of LiTa2PO8

Ion exchange reaction is a promising method to explore metastable compounds that could not be synthesized by conventional high-temperature solid-phase reactions. Herein, a new sodium tantalum phosphate, NaTa2PO8 was synthesized via the Li+/Na+ ion-exchange reaction of the parent compound, LiTa2PO8 in molten NaNO3 medium. NaTa2PO8 underwent an irreversible phase transition from the low- (LT-NaTa2PO8) to the high-temperature polymorph (HT-NaTa2PO8) at approximately 1000 °C. The crystal structures were solved using an ab initio structural determination method based on synchrotron X-ray powder diffraction data. The LT-NaTa2PO8 presented an orthorhombic structure, closely related to that of the parent LiTa2PO8 structure. In contrast, the HT-NaTa2PO8 was found to adopt a monoclinic structure, belonging to a family of monophosphate tungsten bronzes with pentagonal tunnels. The ionic conductivities of LT-NaTa2PO8 (σ = 5 × 10−5 S/cm at 309 °C) and HT-NaTa2PO8 (σ = 2 × 10−7 S/cm at 300 °C) exhibited Arrhenius behavior with activation energies of 0.49 and 0.79 eV, respectively. Bond valence energy landscape (BVEL) calculations indicated that a three-dimensional (3D) conduction pathway is formed in LT-NaTa2PO8 structure, while the conduction pathway in HT-NaTa2PO8 shows a two-dimensional (2D) character.

Synergy of diffraction and spectroscopic techniques to unveil the crystal structure of antimonic acid

The elusive crystal structure of the so-called ‘antimonic acid’ has been investigated by means of robust and state-of-the-art techniques. The synergic results of solid-state magic-angle spinning nuclear magnetic resonance spectroscopy and a combined Rietveld refinement from synchrotron X-ray and neutron powder diffraction data reveal that this compound contains two types of protons, in a pyrochlore-type structure of stoichiometric formula (H3O)1.20(7)H0.77(9)Sb2O6. Some protons belong to heavily delocalized H3O+ subunits, while some H+ are directly bonded to the oxygen atoms of the covalent framework of the pyrochlore structure, with O–H distances close to 1 Å. A proton diffusion mechanism is proposed relying on percolation pathways determined by bond-valence energy landscape analysis. X-ray absorption spectroscopy results corroborate the structural data around Sb5+ ions at short-range order. Thermogravimetric analysis and differential scanning calorimetry endorsed the conclusions on the water content within antimonic acid. Additional 0.7 water molecules per formula were assessed as moisture water by thermal analysis.

Benefit of high-pressure structure on sodium transport properties: Example with NaFeF3 post-perovskite

In the search of promising Na-ion cathode materials, high-pressure synthesis method was applied to obtain sodium iron fluoride NaFeF3 with the post-perovskite lamellar structure. A two-step synthesis was performed: first, the Pnma orthorhombic perovskite structure NaFeF3 form (or Pv-NaFeF3, GdFeO3 type) was synthesized at 1270 ​K and 7.7 ​GPa, then the Cmcm orthorhombic post-perovskite structure (or pPv-NaFeF3, CaIrO3 type) was obtained using a second step at 700 ​K and 15 ​GPa. The post-perovskite form was stabilized under ambient conditions with a low amount of remaining perovskite phase (5 ​mol%). The Mössbauer analysis of pPv-NaFeF3 was firstly investigated with a paramagnetic structure obtained at 300 and 77 ​K, opposed to Pv-NaFeF3 magnetism reflecting the different [FeF6] polyhedra arrangements. Finally, the sodium migration within the framework of both structures was evaluated with the use of Bond Valence Energy Landscape (BVEL) calculations, resulting with an enhanced Na+ mobility within the pPv-NaFeF3 structure.

Lithiation and delithiation induced magnetic switching and electrochemical studies in α-LiFeO2 based Li ion battery

In this work, lithium ferrite synthesized by designed solid-state method was presented, and physical chemistry and battery performance as anode were also studied. Rietveld refinement of the XRD pattern, shows that the diffraction peaks of lithium ferrite can be indexed to the cubic α-phase (Space group Fm-3m). Bond valence energy landscape mapping confirms two dimensional migration pathway of lithium. Effective magnetic moment of 0.55 μB as calculated by Curie-Weiss law justifies the antiferromagnetic ordering for LiFeO2 after charge-discharge reaction. In addition, both the ex-situ XRD and SQUID magnetometry studies reveal a phase (morphology) transition upon the charge-discharge reaction for LiFeO2. The distribution function of relaxation times (DFRTs) analysis confirms that two types of Li ion migrations as originated due to the phase transition in the LiFeO2/lithium coin cell after charge-discharge reaction. Moreover, 4 cycles are needed for attaining capacity ∼600 mAh/g at 0.1C rate. Our work clearly observed the phase (morphology) transition induced magnetic switching in α-LiFeO2 that provides insights into better understanding of the capacity change of electrode materials for the development of high-performance Li-ion battery.

Coupling behavior between lattice dynamics and Li self-diffusion in layered α-LiAlO2 ceramic

In molten carbonate fuel cells (MCFC), α-LiAlO2 ceramic matrix, at higher temperature or H-rich atmosphere, undergoes an irreversible phase transition of α-LiAlO2 to γ-phase that causes a large volume change and greatly impacts the lifetime of the cells. In this manuscript, we unravel an unusual coupling property between the lattice dynamic and Li+ ions diffusion for the first time, near the common operating temperature of 923 K. A temperature-dependent lattice dynamics study on α-LiAlO2 was performed by probing the in-situ Raman spectroscopy. In addition, the phonon density of states was estimated theoretically through first-principles calculations. Notably, in-situ Raman spectroscopy combined with the calculated atom-projected phonons density of states (PDOS) and Bond Valence Energy Landscape (BVEL) calculations demonstrated that the phonon mode Eg dominated by oxygen atoms decays into three acoustical phonons that couple with the diffusion of mobile Li+ ions in ab-plane above 600 K. In MCFC environments, large amounts of Li+ ions or H+ ion in the electrolyte will diffuse into the lattice of α-LiAlO2. This would further enhance the coupling behavior between oxygen atoms and diffusion ion and finally results in the instability of lattice dynamics of oxygen atoms.

Expanding the family of mineral-like anhydrous alkali copper sulfate framework structures: new phases, topological analysis and evaluation of ion migration potentialities

Two novel compounds, K2Cu3(SO4)4 and KNaCu(SO4)2, were synthesized. The crystal structure of K2Cu3(SO4)4 is based on a [Cu3(SO4)4]2− framework with relatively simple bond topology, but with four different CuO n polyhedron geometries. The K+ cations reside in the pores of the framework. The [Cu(SO4)2]2− framework in KNaCu(SO4)2 encloses large elliptical channels running along [001]. Larger channels are occupied by K+, whereas smaller ones are filled by Na+. The bond-valence energy landscape (BVEL) approach has been demonstrated to be a useful method for the prediction of the mobility of alkali metal ions in various structures. By means of this approach, the threshold energies at which isosurfaces begin to percolate as well as the directions of possible ion migration in the structures were determined. The modelling of ion migration maps by the analysis of the procrystal electron-density distribution was used to rapidly identify ion migration pathways and limiting barriers between particular crystallographic sites in the structures under consideration. Its consistency and complementarity with the BVEL method have been demonstrated. Both approaches revealed a relatively low ion threshold percolation and migration barriers in the cryptochalcite-type structures [cryptochalcite: K2Cu5O(SO4)5]. Hence, one may assume that its 3D framework type is suited for ion transport applications. The review of all known members of the groups of anhydrous copper sulfates did not reveal a correlation between the porosity of the framework structures and a manifestation of ion conduction properties.

Origins of dielectric relaxations in AgNb7O18 ceramic

The origins of the relaxor behavior and low-temperature dielectric relaxation processes in AgNb7O18 ceramic were studied and a new relaxation mechanism was proposed through combined bond valence energy landscape (BVEL) calculation and equivalent circuit modeling (ECM). The BVEL calculation suggests that the Ag1 displacement subjects to a double-well potential that originates from the anisotropic coordination symmetry and low coordination number at Ag1 site. The relaxor ferroelectric behavior, observed at 200 K ≤ T ≤ 270 K, is sensitive to thermal history and is ascribed to the Ag1 hopping in double-well potential. The temperature dependence of the matrix capacitance (obtained by ECM) is very similar with that of b axis (obtained by in situ XRD) at 123 K < T < 174 K. Therefore, a phase transition being responsible for the low-temperature dielectric relaxation is assumed. The combined BVEL and ECM techniques performed in this work are therefore quite helpful to understand the complicated relaxor phenomena and explore new relaxors.

Finding the Right Blend: Interplay Between Structure and Sodium Ion Conductivity in the System Na5AlS4-Na4SiS4.

The rational design of high performance sodium solid electrolytes is one of the key challenges in modern battery research. In this work, we identify new sodium ion conductors in the substitution series Na5-xAl1-xSixS4 (0 ≤ x ≤ 1), which are entirely based on earth-abundant elements. These compounds exhibit conductivities ranging from 1.64 · 10−7 for Na4SiS4 to 2.04 · 10−5 for Na8.5(AlS4)0.5(SiS4)1.5 (x = 0.75). We determined the crystal structures of the Na+-ion conductors Na4SiS4 as well as hitherto unknown Na5AlS4 and Na9(AlS4)(SiS4). Na+-ion conduction pathways were calculated by bond valence energy landscape (BVEL) calculations for all new structures highlighting the influence of the local coordination symmetry of sodium ions on the energy landscape within this family. Our findings show that the interplay of charge carrier concentration and low site symmetry of sodium ions can enhance the conductivity by several orders of magnitude.

Charge transport by global protonic conductivity and relaxational dynamics over hydrogen bonds in Fe2+Fe3+3.2(Mn2+,Zn)0.8(PO4)3(OH)4.2(HOH)0.8

This study deals with the charge transport by protons over hydrogen bonds (HBs) in a rockbridgeite-type compound, Fe2+Fe3+3.2(Mn2+,Zn)0.8(PO4)3(OH)4.2(HOH)0.8. Its dielectric response in a wide frequency range of 1 Hz – 3 GHz from 30 K to 500 K can be traced back to structural properties of this phosphatic oxyhydroxide, revealed by Rietveld refinements using neutron powder diffraction data. The probable charge transport paths for protons are proposed, based on the honeycomb-like distribution of their neutron scattering length densities reconstructed by the Maximum-Entropy Method. Two distinctly decoupled proton dynamic processes occur in this system: at high temperatures, global protonic transport is thermally activated over an energy barrier (EB) of 0.49 eV, showing a dc conductivity (σdc) value of about 10-4 Ω-1 cm-1 at 500 K. The temperature-dependency of σdc becomes weaker at decreased temperatures, indicating the possible onset of proton tunneling-dominated charge transport. At low temperatures, relaxational proton hopping within double-well potentials in HBs is thermally activated with EB = 0.62 eV. An extremely fast relaxation time of ~50 ps at 250 K continuously slows down to ~1 ms at 150 K, pointing to the approach of an orientational proton-glass state at about 125 K. Isosurfaces of bond valence energy landscape maps of H+ at 0.49 eV clearly evidence the honeycomb-shaped route for the protonic conductivity at 393 K.

Structural and electrochemical investigation of lithium ions insertion processes in polyanionic compounds of lithium and transition metals

The paper considers approaches to the synthesis as well as the structural and electrochemical properties of lithium and transition metals polyanionic compounds as promising cathode materials for lithium-ion battery. The characteristics of lithium and transition metals sulfates are considered, among which iron-lithium sulfate and a composite electrode material Li2Fe(SO4)2/C based on it was selected for further detailed study. The relationships between the synthesis conditions and the structural and electrochemical characteristics of the material were revealed. Based on the structural data the computational method of the bond valence strengths (BVS) applying the bond valence energy landscape algorithm (BVEL) provided activation energy maps of lithium ion migration in the Li2Fe(SO4)2 crystal structure. The method of scanning electron microscopy (SEM) made it possible to characterize the morphological state of the material, to determine the particle size distribution, which were then used to determine the geometry of the diffusion space of particles. Applying the electrochemical kinetics investigation methods (CV, GITT, EIS) the parameters of lithium ion transport in the electrodes were determined. The quasi-equilibrium E(c) dependence of the Li2Fe(SO4)2/C electrode was obtained, this dependence was simulated using an approach based on the Frumkin intercalation isotherm and the lattice gas model, and the thermodynamic characteristics of the interparticle interaction in the material were obtained. The diffusion coefficient of lithium ions D in the material was estimated using the CV method: 1.6·10−15 cm2·s−1 in the anodic half cycle and 10−15 cm2·s−1 in the cathodic half cycle, respectively. The dependences of D on the lithium ion concentration in the intercalate and electrode potential were obtained using GITT and EIS methods, a comparison of these methods results was performed.

Li+ conduction in air-stable Sb-Substituted Li4SnS4 for all-solid-state Li-Ion batteries

Development of new sulfide Li+ superionic conductors with mechanical sinterability is the key to the success of all-solid-state lithium batteries. While phosphorus-containing sulfide superionic conductor materials have been widely investigated, phosphorus-free materials showing good air-stability have been overlooked. Herein, the Li+ dynamics in Sb-substituted Li4SnS4 showing a high Li+ conductivity of max. 0.85 mS cm−1 at 30 °C and excellent dry-air stability as well as negligible H2S evolution is described. Structural analysis with X-ray and neutron diffraction reveals that Sb-substitution renders an expansion of the lattice volume and formation of Li vacancies. Additionally, 1D-preferable 3D Li+ diffusion channels in Li4-xSn1-xSbxS4 are disclosed. The fast Li+ diffusion in Li4-xSn1-xSbxS4 is rationalized by complementary analysis using AC impedance measurements, bond valence energy landscape calculation, and 7Li nuclear magnetic resonance spectroscopy. Excellent electrochemical performances of TiS2 electrodes employing Li3.85Sn0.85Sb0.15S4 in all-solid-state batteries are demonstrated.