Lithium penetration in garnet-type Li7La3Zr2O12 (LLZO) is frequently discussed using a single dendrite picture, although practical failure can also involve whisker-like protrusions, percolating metallic networks, and abrupt filamentary shorting. Here we develop a compact theory that separates morphology selection from connectivity evolution and reconnects them through current density, an engineering-completeness disorder coordinate, and electronic leakage. A transport-heterogeneity parameter governs the transition from planar deposition to whisker-like or dendritic growth, whereas a connectivity order parameter p(t)∈[0,1] tracks the buildup of system-spanning metallic pathways. The observed critical current density (CCD) corresponds physically to the crossing of the percolation threshold pc(Δ), at which a spanning metallic pathway first appears across the electrolyte; a higher current Jfil>JCCD identifies the mature-filament threshold at which the connectivity order parameter reaches the higher level pf>pc. In this framework, whisker, dendrite, percolation, and filament are not mandatory sequential stages but competing outcomes within a unified instability landscape. The effective disorder parameter Δ is interpreted as an engineering-completeness coordinate that compresses microstructural roughness, interfacial nonuniformity, contact pressure, and protocol variability into a single scalar; operating temperature is handled independently through an explicit Arrhenius factor with effective activation energy Eaeff. The model is calibrated against four representative LLZO benchmarks spanning both the engineering-completeness axis and two operating temperatures: Flatscher et al. (no engineering, 25 °C, 0.28mAcm-2), Kim et al. (interface-engineered LLZO at 25 °C, 1.6mAcm-2, and at 60 °C, 2.6mAcm-2), and Taylor et al. (high-current cycling at 60 °C, 6.0mAcm-2). The Kim RT/60 °C pair at fixed Δ fixes Eaeff≈0.11 eV independently of the Δ-dependence. All four benchmarks are reproduced within approximately 15%. From CCD data alone, the four prefactors C, A, a2, and a3 enter only through the identifiable combination Λ=C[a3/(a2A)]1/(m+1); individually they are structurally non-identifiable. We hold C=1 as normalization and (a1,a2,a3) at fixed structural values, and fit A directly as an effective scale conditional on those choices. The framework explains why apparent CCD values are protocol dependent and why morphology-instability onset need not coincide with electrical shorting. Beyond the qualitative phenomenology, we provide a classified parameter identifiability map, specify the validity domain of the saturation approximation used in deriving JCCD, discuss regime-dependent connectivity signatures, and identify the post-shorting temporal interval between initial percolation and mature-filament threshold crossing (≈1.5–4.5 dimensionless effective time units across the LLZO engineering-completeness axis). The model identifies a dual role of disorder: it amplifies local flux heterogeneity and lowers the effective threshold for metallic Li connectivity. These results provide a microstructure-informed interpretation of CCD in garnet electrolytes, generate experimentally testable predictions for pulse-current and interface-engineering studies, and suggest design principles for suppressing lithium penetration in ceramic solid electrolytes.
In this work, we present a modified Poisson-Nernst–Planck (PNP) framework to describe the electrokinetic response of blocking electrodes exhibiting combined resistive and capacitive dispersion. The model introduces two extensions: (i) a finite time delay Δτ accounting for the non-instantaneous response of ionic fluxes to gradients of concentrations and of the electric field, and (ii) a fractional time derivative of order α in the continuity equation to capture the broad distribution of relaxation times. We derive the analytical impedance function for a one-dimensional symmetric electrolyte bounded by perfectly blocking electrodes. We show that this impedance displays a constant phase element (CPE) behavior at low frequencies controlled by the fractional order α, while the delay Δτ captures the transition to mid-frequency resistive behavior, as observed in real electrochemical systems. The proposed model provides a foundation for interpreting the impedance spectra of porous electrodes, and can be readily extended to describe other electrode systems with more complex geometries and compositions.
A detailed study is presented of the electrochemical ion-exchange of Li+ for Na+ in O3-type NaNi0.6Mn0.2Co0.2O2 (NaNMC) to form LiNi0.6Mn0.2Co0.2O2 (LiNMC). The ion exchange was conducted in incremental steps by cycling NaNMC in a Li half-cell, allowing a detailed analysis of the mechanism involved. It was found that during cycling NaNMC in a Li half-cell, P3-[NaxLiy□1-x-y]NMC was formed, which decomposed into O3-LiNMC after a critical number of vacancies was reached. A simple model based on this mechanism successfully predicted the ion exchange behavior of NaNMC for different ion-exchange cycling conditions. The resulting LiNMC materials made by ion exchange were found to have reversible capacities of ∼130–140 mAh/g with good cycling retention over 100 cycles. These results give insights into the mechanisms for electrochemical ion exchange and show that electrochemical ion-exchange is a promising method for the synthesis and exploration of novel cathode materials.
Molecular crystal electrolytes offer a unique advantage in that ion-transport behavior can be directly correlated with structural and dynamical changes in the solid state. In this study, sulfolane (SL)-based molecular crystals prepared with various lithium salts were systematically investigated to explore novel molecular crystal electrolytes and elucidate the origin of phase-dependent ionic transport. While lithium bis(fluorosulfonyl)amide (LiFSA) and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) formed molecular crystals only within limited compositional ranges, lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide (LiCFSA) enabled crystallization over a wider composition range. Among these materials, Li(CFSA)(SL)3 exhibited an ionic conductivity of 7.4 × 10−7 S cm−1 at 25 °C. Li+ transference-number measurements revealed a high Li+ transference number of 0.95, indicating that Li+ is the dominant mobile charge carrier. Thermal analysis revealed that Li(CFSA)(SL)3 undergoes a distinct solid-solid phase transition at −3.8 °C, clearly separated from melting at 53.8 °C. Temperature-dependent conductivity measurements demonstrated a discontinuous change in ionic conductivity across the phase transition. Le Bail analysis of powder XRD patterns suggests that the hexagonal framework is retained while structural symmetry is enhanced across the transition. Concurrently, Raman spectroscopy reveals an increase in the motional freedom of both SL molecules and CFSA anions. These results suggest that the phase transition is accompanied by changes in lattice dynamics and local coordination environments that contribute to enhanced ionic transport while maintaining crystallinity. This study demonstrates that solid–solid phase transitions can effectively regulate ionic transport in molecular crystal electrolytes and highlights phase-dependent lattice dynamics as an important design principle for developing advanced molecular crystal electrolytes.
Composite gel polymer electrolytes based on a perfluorinated sulfonic acid cation-exchange MF-4SC membrane containing surface-sulfonated nanoparticles of aluminum oxide, cerium (IV) oxide, and titanium oxide (sAl2O3, sCeO2, and sTiO2, respectively) were prepared by casting from a dispersion in N,N-dimethylformamide and plasticized with a 1,3-dioxolane/1,2-dimethoxyethane mixture. The influence of the filler nature on ionic conductivity, solvent uptake, activation energy, lithium transference numbers, and electrochemical stability was investigated. The membrane with sAl₂O₃ exhibits the highest conductivity (1.0 × 10−4 S cm−1 at 25 °C). In symmetric Li||Li cells, all membranes provide stable cycling for over 600 h. The Li+ transference numbers reach 0.83–0.87, which substantially exceed those of liquid electrolytes. LiFePO₄||Li cells with all composite electrolytes revealed an initial discharge capacity of up to ∼150 mAh g−1 (at 0.1C rate). The effect of membrane composition on a Coulombic efficiency and cycling stability is discussed. The obtained results demonstrate the promise of modified MF-4SC membranes as gel polymer electrolytes for lithium metal batteries.
In this work, the effects of BaO-NiO-TeO2 composite sintering additive on the sintering behavior, crystal structure and electrical properties of BaZr0.5Ce0.3Y0.2O3-δ (BZCY) proton conductor were systematically investigated. A series of BZCY samples incorporated with 0, 1, 2 and 3 mol% BaO-NiO-TeO2 sintering additive, along with control samples singly doped with NiO or BaO–TeO2, were synthesized via the conventional solid-state reaction method.Microstructure analysis and electrochemical measurements revealed that the introduction of 2 mol% composite sintering additive (denoted as BZCY-2) effectively lowered the sintering densification temperature to 1450 °C, along with simultaneous improvements in the average grain size and electrical conductivity of the sample. Further calculations demonstrate that the enhanced conductivity of BZCY-2 originates from its higher apparent grain boundary conductivity, which is mainly ascribed to a reduced space charge potential. In wet air, BZCY-2 achieved a total conductivity of 4.11 × 10−3 S·cm−1 at 700 °C. Calculated using the defect equilibrium model, the proton transference number of BZCY-2 at 700 °C was determined to be 0.68, which is higher than that of BZCY doped with NiO alone.The ternary composite additive system developed in this work promotes grain growth via the low-temperature liquid-phase sintering of TeO2, while mitigating additive residue at grain boundaries through its high-temperature volatilization. Combined with the Ba vacancy compensation effect of BaO and the sintering promotion effect of NiO, this ternary system holds great application prospect as a high-efficiency composite sintering additive.
With this series of proceedings-perspective articles, the journal Solid State Ionics introduces a novel format of progress reports from the research community that aims to bridge the gap between traditional conference proceedings and perspective articles. In addition, it has become apparent in recent years that traditional conference proceedings papers (presumably also favoured by a significant acceleration in scientific publishing) no longer meet the response that was the case in earlier times.This new paper format is an attempt to meet the needs of researchers in a modern publication environment to report the latest developments at the forefront of science (as they are usually discussed at conferences), which are thus brought into a citable form as soon as possible. We thus believe that this innovative format offers several advantages: It accelerates the dissemination of cutting-edge research, provides strategic guidance on promising research directions, increases the visibility of key conference papers, delivers efficiently curated content to readers, and provides a good balance between timely coverage and scientific depth.The E-MRS 2025 Spring Meeting Symposium K on “Solid state ionics: functional materials and devices for electrochemical energy conversion and storage applications” serves as the first conference where the Solid State Ionics community is exploring this innovative publication approach. Rather than providing exhaustive coverage of all presentations, this new format of proceedings-perspective papers highlights key developments and emerging research directions within the field of solid state ionics as identified by leading contributors in each subfield. Each paper focuses on one of the following four central topics.Defect Engineering & Surface Chemistry.Solid Oxide Cells.Protonics & Reactors.Batteries.
The perovskite oxides have attracted considerable attention as cathode materials in intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their enhanced oxygen transport kinetics and high oxygen diffusion coefficients. This study focuses on the perovskite PrBa0.5Sr0.5Co2-xCrxO5+δ (0 ≤ x ≤ 0.20) and systematically investigates the influence of chromium doping concentration on its structural properties, electrical conductivity, and electrochemical performance, aiming to reduce the thermal expansion coefficient and improve the cathode efficiency. A series of samples were successfully synthesized using a sol-gel combustion method. X-ray diffraction and Rietveld refinement results indicate that all samples retain a pure cubic perovskite structure. and exhibit good chemical compatibility with the Ce0.8Sm0.8O1.9 (SDC) electrolyte at 1100 °C. The average thermal expansion coefficient (TEC) of the material decreases significantly from 17.67 to 12.54 × 10−6 K−1 as the chromium doping level increases. The symmetric cell with the PBSCCr0.10 cathode shows a polarization resistance (Rp) of 0.074 Ω cm2 at 800 °C, with an activation energy of 119.96 kJ mol−1. The single cell with PBSCCr0.10 cathode achieves a power density of 0.988 W cm−2 at 800 °C. These results demonstrate that PrBa0.5Sr0.5Co1.9Cr0.1O5+δ (PBSCCr0.10) is a highly promising cathode material for intermediate-temperature solid oxide fuel cells, highlighting the effectiveness of the B-site doping optimization.
NaNbO3(NN)-based antiferroelectric ceramics were modified by oxygen-atmosphere annealing to regulate oxygen vacancy concentration and tailor oxygen octahedral distortion for improved energy storage performance. Oxygen vacancies induce local charge imbalance and cation displacement, leading to octahedral distortion that strongly affects phase stability and polarization behavior. Oxygen annealing effectively reduced vacancy concentration and alleviated octahedral distortion, as evidenced by an increase in the O1-Nb-O2 bond angle from 155° to 168°. Among Na0.85Bi0.05Nb(1–0.2x)MgxO3 ceramics (x = 0.10–0.25), the x = 0.15 composition exhibited the best overall performance, achieving a recoverable energy density of 1.59 J cm−3 and an efficiency of 64% at an experimentally observed breakdown field of 170 kV cm−1, together with characteristic double P-E loops and good short-term repeatability over three consecutive cycles. These results reveal strong coupling between oxygen vacancy-regulated octahedral distortion and macroscopic energy storage behavior, providing guidance for designing high-performance lead-free dielectric ceramics.
To address the severe interfacial side reactions and sluggish ion transport between high‑nickel cathode Ni0.8Co0.1Mn0.1O2 (NCM811) and sulfide solid electrolyte Li6PS5Cl (LPSC) in all-solid-state batteries, a uniform PSSLi polymer coating layer with a thickness of ∼30 nm is constructed on the NCM811 surface via a solution method. The PSSLi coating effectively suppresses direct interfacial contact between the cathode and electrolyte while accommodating volume variation owing to its intrinsic flexibility. The modified cathode delivers a discharge capacity of 113 mA h g−1 at 2C and retains 128 mA h g−1 after 100 cycles at 0.5C, corresponding to a capacity retention of 84%. Moreover, the Galvanostatic intermittent titration technique and Distribution of relaxation times analyses reveal enhanced Li+ diffusion kinetics and reduced interfacial resistance. The improved performance is attributed to the combined effects of interfacial stabilization and facilitated Li+ transport enabled by the single-ion conductive of PSSLi coating. This work provides an effective strategy for interface engineering of high‑nickel cathodes in sulfide-based all-solid-state batteries.
Electronic structure calculations were undertaken to elucidate the primary hydration, proton dissociation, and subsequent proton transport in bipolar membranes (BPMs) under minimal hydration conditions. Specifically, the terminal head groups of a proton exchange membrane (PEM), anion exchange membrane (AEM), the catalyst layer, and the interfaces (catalyst/PEM, and catalyst/AEM) of a BPM were examined. Fully optimized structures at the B3LYP/6-311G** level of theory with the inclusion of a dielectric continuum solvation model (SMD) to account for the water were undertaken. Water molecules were added to the system explicitly from n = 1-8, which leads to the dissociation of protons from the head groups in PEM, catalyst, and interface (catalyst/PEM, and catalyst/AEM) systems and hydration of hydroxide ion in an AEM system forming OH- (H2O)2/OH- (H2O)3 complexes. Upon dissociation the hydrated proton exists as one of the three cation configurations: a Zundel or Eigen-like or Eigen depending on the degree of hydration. The potential energy surface scans at the same level of theory (with SMD) indicates that the energetics associated with the proton transfer from the protonated water to water or from water to hydroxide goes via a Zundel cation [H2O-H*-OH2]+ or via [HO-H*-OH] - complex configuration at the transition state. The results indicate that once a proton is transferred from the donating to the accepting oxygen atom, it preferentially remains with the accepting oxygen atom and achieves a local minima structure. The calculated energy barrier for proton transfer from a hydrated proton to H2O is about a third of that for proton transfer from H2O to a hydroxide ion. This fundamental study may serve to provide molecular insights for different layers and interfaces of BPMs.
Flash sintering of electrically insulating multicomponent oxide systems remains challenging due to their low intrinsic conductivity. In this study, flash sintering of a SiO2-HfO2-ZrO2 ternary system was enabled using 8YSZ as a conductive phase, and the influence of current density on densification, phase evolution, and dielectric properties was systematically investigated. Flash onset occurred at ∼987 °C under an applied electric field of 200 V/cm for a powder mixture containing 50 wt.% HfO2-SiO2 (equimolar) and 50 wt.% 8YSZ. Isothermal flash sintering at 1000 °C with current densities ranging from 60 to 180 mA/mm2 resulted in rapid densification (in a few seconds), achieving a maximum relative density of ∼94%. Increasing current density promoted enhanced dissolution of HfO2 into the ZrO2 lattice, leading to the formation of a (Hf,Zr)O2 solid solution. This compositional modification reduced the effectiveness of yttria in stabilizing the cubic fluorite phase triggering cubic-to-tetragonal prime (c → t') phase transformation at higher current densities. The transformation was rapid, occurred within 5 s in flash state. Microstructural and spectroscopic analyses confirmed the absence of crystalline silicate phases. The dielectric response exhibited strong dependence on phase composition and defect chemistry, with the highest dielectric constant observed in the cubic phase regime (k ≈ 35 at 400 °C), followed by a reduction upon formation of the t' phase. The dielectric relaxation behaviour was governed by thermally activated oxygen vacancy migration. These findings demonstrate that the conductive phase plays a critical role in enabling flash sintering and controlling phase stability, defect evolution, and functional properties in multicomponent oxide systems.
Metal–organic frameworks (MOFs) are promising host materials for studying and controlling the dynamics of molecules and ions, including lithium ions. In this study, a lithium-ion-containing ionic liquid (IL) was successfully incorporated into the MOF ZIF-8, and its phase behavior and ionic conductivity were investigated. Using a capillary action method, lithium bis(trifluoromethanesulfonyl)imide (Li[TFSI])-containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][TFSI]), denoted as Li0.2[Emim]0.8[TFSI], was introduced into the pores of ZIF-8. The impact of varying Li0.2[Emim]0.8[TFSI] concentrations on the crystal structure, bond vibrations, and ionic conductivity was systematically analysed. Structural analysis revealed an increase in the lattice constant of ZIF-8 upon Li0.2[Emim]0.8[TFSI] encapsulation, accompanied by a weakening of the N–Zn–N bond as the cage structure expanded. Additionally, the migration of Li[TFSI] ion pairs into the cages disrupts ion pair interactions, leading to a reduction in the O=S=O bond strength within the [TFSI]− anion. When the ZIF-8 pores were fully saturated with Li0.2[Emim]0.8[TFSI], the composite exhibited an ionic conductivity of 0.36(2) mS·cm−1 at 80 °C, with the activation energy of 0.26(1) eV. Its ionic conductivity meets the performance criteria required for use in lithium-ion battery electrolytes. However, it has the low lithium transference number. And the LiCoO2||Li coin cells with LEI1.2@ZIF pellet has a capacity retention of 74.9% only after 100 cycles at 0.2C at room temperature. Compared with the pure lithium-salt-containing ionic liquid, Li0.2[Emim]0.8[TFSI], the quasi-solid-state electrolyte LEI1.2@ZIF, prepared by incorporating the lithium-salt-containing ionic liquid into the ZIF-8 framework, exhibits inferior electrochemical performance in lithium batteries. This is primarily due to the ionic conductivity that is two orders of magnitude lower and a higher interfacial impedance of the quasi-solid-state electrolyte LEI1.2@ZIF. These findings highlight the potential of MOF-based composites as quasi-solid-state or solid-state electrolytes for lithium-ion battery applications.
The partial electronic conductivity (bel) in Li solid electrolytes (SEs) has important implications in determining the self-discharge rate and degradation processes of solid-state batteries, but reliable scientific data on the electronic transport properties of Li SEs remain scarce. While Hebb-Wagner polarization measurement using asymmetric cells with a single ionic-blocking electrode has been reported as a powerful technique to probe bel at different Li activities, we suggest that it is not suitable for probing the intrinsic electronic transport properties of lithium thiophosphate-based SEs due to unavoidable anodic decomposition of the SE. Polarization using doubleblocking-electrode cells is, therefore, proposed as a more appropriate technique to determine the bel at a specific Li activity related to the Li activity of the unpolarized SE. Using temperature-dependent double-blocking-electrode polarization, we examine the electronic transport properties of common lithium thiophosphate glass and glass-ceramic SEs, including Li3PS4 and Li7P3S11 glasses; Li3PS4 and Li7P3S11 glass-ceramics with varying crystallinity, as well as Cl-doped and N-doped Li3PS4 glasses with varying dopant concentrations. The results provide a reliable basis to investigate the effect of annealing and doping conditions on the electronic transport properties. Among all conditions, N3- doping was found to exhibit the largest effect on increasing bel. Moreover, all SEs studied in this work exhibit two distinct linear regimes in the Arrhenius plots of bel: a low-temperature regime with a lower activation energy, and a high-temperature regime with a higher activation energy. These findings provide important insights into understanding the electronic transport and conduction mechanisms in lithium thiophosphate-based SEs.
Ionic liquids (ILs) and deep eutectic solvents (DESs) have attracted significant attention as alternative electrolytes for energy storage systems owing to their non-flammability, low volatility, low toxicity, and excellent thermal, chemical, and electrochemical stability. Nevertheless, the widespread utilization of ILs is hindered by their high cost, whereas DESs, although economically attractive and simple to synthesize, often exhibit comparatively lower ionic conductivity and narrower electrochemical stability windows. To combine the advantages of both systems while maintaining economic feasibility, a small amount of IL can be incorporated as a functional additive into a DES matrix. In the present work, 1-ethyl-3-methylimidazolium dicyanamide (EMIMDCA) was introduced into a phenyltrimethylammonium chloride/phenol (1:3) deep eutectic solvent to develop a cost-effective electrolyte system with improved transport properties. The physicochemical behavior of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a DES with added EMIMDCA was systematically investigated. Density, viscosity, and specific conductance measurements were carried out over a range of LiTFSI molalities and temperatures. From density data, apparent molar volumes (Vϕ) and partial molar volumes (Vϕ0) were determined to elucidate solute-solvent interactions. Molar conductivity (Λm) and limiting molar conductance Λmowere evaluated to assess ion transport and structural characteristics of LiTFSI in the solvent system. Fourier transform infrared (FT-IR) spectroscopic analysis was performed to investigate the structural changes involved in the formation of the DES. The electrochemical stability of the systems under investigation was evaluated using cyclic voltammetry measurements.
Solid-state sodium-metal batteries (SSSMBs) are regarded as promising next-generation energy storage systems, but their development is limited by the brittleness of inorganic electrolytes and the low room-temperature ionic conductivity of polymer electrolytes. Herein, a three-dimensional porous sodium-ion conductive framework was fabricated through a facile, one-step sacrificial template strategy using Na3Zr2Si2PO12 (NZSP) and polyvinyl alcohol (PVA). After infiltration with a quasi-solid-state phase composed of PEO, NaTFSI, and Pyr14TFSI, a hybrid electrolyte with combined ceramic/polymer ion-transport pathways was obtained. Among the investigated samples, the optimized 3D-80RPNZSP exhibited an ionic conductivity of 0.331 mS cm- 1 at 30 degrees C and a wide electrochemical stability window of 4.64 V. The improved electrochemical performance is attributed to the combined effects of the interconnected porous NZSP framework and the ionic-liquid-containing phase, which together promote electrolyte infiltration and reduce the overall ion-transport resistance. In Na||Na symmetric cells, the 3D-80RPNZSP electrolyte enabled stable Na plating/stripping for over 1000 h at 0.02 mA cm- 2. In Na3V2(PO4)3|Na full cells, a capacity retention of 90.85% was achieved after 200 cycles at 0.5C and 30 degrees C. This work provides a simple and effective methodology for developing porous NZSP-based hybrid electrolytes for solid-state sodium-metal batteries.
