Soon-Ki Jeong

Solid electrolyte interphase (SEI) characterization is needed to interpret the performance, degradation, and lifetime of graphite and Si-containing carbon-based negative electrodes in lithium-ion batteries. However, SEI claims are often difficult to compare because measured signals, inferred assignments, sample history, and electrode architecture are not always clearly separated. This review presents a claim-bounded framework for SEI characterization that distinguishes direct observables from inferred chemical, molecular, structural, morphological, and functional information. Photoelectron spectroscopy methods provide chemical-state and relative-depth-sensitivity constraints; secondary-ion mass spectrometry methods provide fragment and isotope distributions; vibrational spectroscopies support functional-group and local vibrational evidence; nuclear magnetic resonance and molecular mass spectrometry provide molecular or product-level constraints; and microscopy, tomography, and atomic force microscopy provide morphology, architecture, local thickness, topography, and mechanical response. Across these methods, rinsing, drying, sputtering, beam exposure, extraction, and limited sampling can alter the observable and therefore the defensible claim. The review emphasizes the distinction between native electrode-associated SEI features and extracted, soluble, or electrolyte-phase products, and between morphology-only evidence and chemically assigned morphology. It concludes by proposing claim-driven correlative workflows and reporting guidance for reproducible interpretation on graphite, Si/graphite, Si/C, and carbon-coated Si architectures where directly studied or present.

Anodic corrosion of Al alloy electrodes limits their use as anodes in alkaline aluminum–air batteries. Na₂SO₄- and Al₂(SO₄)₃-containing formulations were compared at matched nominal sulfate-group inputs but different formulation-derived Na and Al inputs. Aqueous 2 M NaOH was mixed with 0.3 M Na₂SO₄ or 0.1 M Al₂(SO₄)₃ solution at NaOH:additive-solution volume ratios of 7:3, 5:5, and 3:7, and Al–Mg–Sn–Gd–P alloy electrodes were evaluated in a three-electrode configuration. All galvanostatic tests passed the same external charge of 160 mAh. Mass-loss-normalized anodic charge (Q_Δm) is reported as an operational metric normalized by the net post-discharge electrode mass decrease, not as conventional battery capacity or efficiency. The Al₂(SO₄)₃-containing formulations showed higher Q_Δm values; at the 3:7 ratio, Q_Δm increased from 917 to 1894 mAh g⁻¹. Potentiodynamic polarization yielded lower polarization-derived apparent corrosion current densities and higher polarization resistances, while potentiostatic electrochemical impedance spectroscopy showed larger interfacial impedance responses in the Al₂(SO₄)₃-containing series. Scanning electron microscopy showed electrolyte-dependent post-discharge morphologies. These results establish sulfate-source-dependent differences in anodic, polarization, impedance, and morphological responses under matched nominal sulfate-group input without isolating the effect of a single Na- or Al-containing species, establishing the presence or chemical identity of a distinct interfacial film, or demonstrating improved full-cell performance.

This study investigates the effect of electrolyte concentration on the crystal structure and electrochemical performance of copper hexacyanoferrate (CuHCF) as an electrode material for aqueous zinc-ion batteries. CuHCF electrodes were tested in ZnCl ₂ electrolytes with concentrations ranging from 1.0 to 10.0 mol dm⁻ ³ . Electrochemical analyses—including linear sweep voltammetry and galvanostatic cycling—revealed a strong dependence of capacity and cycling stability on electrolyte concentration. The 1.0 M electrolyte exhibited superior initial capacity, whereas the 10.0 M electrolyte demonstrated enhanced capacity retention during prolonged cycling. X-ray diffraction showed that higher concentrations suppressed Zn-ion substitution in the CuHCF lattice, thereby improving structural stability. These findings suggest that careful tuning of electrolyte concentration is critical for balancing initial performance and long-term durability in CuHCF-based zinc-ion batteries.

Silicon oxide–carbon (SiOx–C) negative electrodes exhibit diminished performance at reduced temperature. This study isolates the role of electrolyte salt in EC/DMC half‑cells by holding the electrode formulation, separator, potential window, and current density constant and comparing 25°C and 15°C. Galvanostatic profiles and electrochemical impedance spectroscopy were used to quantify polarization, capacity, and interfacial resistance. On lowering to 15°C, all salts showed increased polarization; the severity followed LiCF ₃ SO ₃ ≳ LiClO ₄ > LiPF ₆ ≫ LiBF ₄ . Nyquist spectra exhibited the same ordering in the growth of the mid‑frequency arc. At 25°C, the durable capacity ranking was LiBF ₄ > LiPF ₆ > LiClO ₄ > LiCF ₃ SO ₃ . Under the fixed protocol, capacities at 15°C collapsed toward low values for all salts, indicating a kinetic penalty sufficient to trigger premature voltage cutoffs. LiBF ₄ minimized the increase in interfacial resistance but did not preserve capacity at 15°C. The data show salt-dependent low-temperature kinetics in SiOx–C and indicate that operation near 15°C requires lower current density, adjusted potential windows, or deliberate control of interphase and solvation chemistry.

Ethylene carbonate (EC) is essential for establishing a passivating surface film on graphite; in practice, however, EC is commonly blended with dimethyl carbonate (DMC), which alters Li ⁺ solvation and interfacial chemistry. Here, we compare 1 mol dm ^{− 3} (M) LiClO ₄ /EC+DMC with 1 M LiClO ₄ /DMC using in situ electrochemical atomic force microscopy (AFM) during cyclic voltammetry on the basal plane of highly oriented pyrolytic graphite (HOPG). Both media follow a two-stage pathway—solvent cointercalation (subsurface pre-insertion) followed by surface precipitate formation—yet their electrochemical responses and morphologies diverge. In EC+DMC, pronounced second-cycle suppression of the cathodic current accompanies the development of a laterally continuous, fine particulate precipitate layer after the first cycle. In the DMC‑only electrolyte, large cathodic currents persist and AFM reveals edge-dominated blistering, step disruption, and patchy deposits, indicative of sustained cointercalation and incomplete passivation. Taken together, these results indicate that the principal passivating film is EC-derived, whereas DMC chiefly modulates cointercalation and coalescence kinetics, thereby amplifying lateral heterogeneity. The measurements provide potential-resolved benchmarks for formation-protocol design and a reference for interpreting mixed-carbonate electrolytes.

Calcium-ion batteries are emerging as a sustainable and high-energy alternative to lithium systems, yet the atomic-scale origin of their ion–host interactions remains unclear. We clarified the coupling between ion mobility and electronic structure in titanium disulfide (TiS ₂ ) by combining multiscale density functional theory with experimental analysis. Periodic VASP simulations and localized DV-Xα analyses revealed that Ca ²⁺ intercalation induces greater lattice expansion than Li ⁺ , lowers diffusion barriers, and enriches the density of states near the Fermi level, enhancing both ionic and electronic transport. Despite weaker Ca–S interactions, strong Ti–S covalency stabilizes the framework, yielding a theoretical open-circuit voltage of 1.383 V, which is lower than that of LiTiS ₂ (1.948 V). Orbital overlap and charge-transfer analyses show that this lower voltage reflects a balance between multi-electron charge storage (z = 2 for Ca ²⁺ ) and moderated electronic restructuring, rather than a simple reduction in electrochemical performance. Electrochemical measurements confirm these results: Ca-intercalated TiS ₂ delivers a first-cycle capacity of 201 mAh·g ^− 1 , superior diffusion coefficients, and 96.3% rate retention with stable cycling. This work provides the first atomistic evidence that Ca ²⁺ insertion facilitates ion transport while imparting structural resilience, offering a design framework for next-generation multivalent-ion batteries.

This study reports a graphite-core, multiphase gradient C–Si–N composite architecture for Si-containing graphite-based negative electrodes in lithium-ion batteries. The increase in electrode thickness is used as a practical metric of expansion-driven degradation. The composite is prepared by the simultaneous nitridation and carbonization of a graphite core–Si precursor using polyvinylpyrrolidone (PVP) as the N source. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy indicates a quasi-continuous radial trend in the relative N signal toward the outer shell, consistent with preferential N enrichment near the particle exterior. This spatially distributed N arrangement may spatially separate the Si-rich expansion-prone region from the carbon-rich exterior containing nitrides and other N-bearing species, thereby enabling stress partitioning. The shell architecture is designed to disperse expansion-induced stress and stabilize the electrode–electrolyte interface. During electrochemical cycling, the C–Si–N electrode with 10% PVP preserves its core–shell morphology and exhibits the smallest average electrode thickness expansion (~58% after 40 cycles, based on four independent cells). The reduced thickness growth is discussed in relation to a mechanically robust Si–N matrix (Si₃N₄-like/SiN_x-like), potential Li–N interphase species, and N-containing carbon, together with the post-mortem morphology and electrochemical impedance evolution. This study presents reduced swelling as an electrode-level trend versus nominal PVP addition, along with associated nitride-related signatures, thereby highlighting spatially graded stress buffering as an electrode-level design principle.

Ethylene carbonate (EC) is essential for forming a passivating film on graphite, whereas practical electrolytes dilute EC with linear carbonates that modify that film. Here, we isolate an EC-only medium and track film formation by in situ electrochemical atomic force microscopy during slow-scan cyclic voltammetry on the basal plane of highly oriented pyrolytic graphite in EC with lithium perchlorate. A two-stage pathway is resolved: during the cathodic sweep a subsurface pre-insertion regime develops and transitions near 0.8 V vs Li/Li ⁺ ; the subsequent anodic sweep produces a particulate precipitate layer. After the first cycle, the effective precipitate-layer thickness is approximately 20 nm; a second cycle increases it to approximately 30 nm with marked lateral heterogeneity and edge-proximal coarsening. These observations delineate the potential-dependent switch and provide quantitative benchmarks for the early growth of the EC-derived film. Minimizing the dwell time near the transition may suppress overgrowth and improve interfacial stability, thereby establishing an EC-only baseline for interpreting mixed-carbonate electrolytes.

The electrochemical reuse of spent graphite from the negative electrodes of lithium-ion batteries is influenced by regeneration-induced changes in near-surface chemical and defect states. These states govern solid electrolyte interphase (SEI) re-formation, particularly when bulk contaminants are suppressed. Acidic malic-acid leaching and ethylenediaminetetraacetic acid chelation under alkaline conditions (pH 8.7) were compared under similar operating parameters to isolate the role of the leaching environment. This was followed by heat treatment at 1200 °C to decouple chemical cleaning from structural restoration. Both methods reduced the total impurities from 217.85 ppm to ~1.8 ppm, approaching that of commercial graphite. Despite the comparable bulk purity, depth-resolved X-ray photoelectron spectroscopy after formation cycling revealed distinct outermost surface states relevant to SEI re-formation: acidic processing yielded a more oxygenated carbon signature and higher LiOH fraction at the outermost surface (~16%), whereas alkaline chelation produced a more graphitic, carbonate-dominated surface with lower LiOH (~7%). Electrochemical and impedance measurements were consistent with these differences, suggesting that after the bulk impurities were minimized, resistance development was largely governed by the leaching-conditioned near-surface state, which biased the SEI composition. The comparison under matched conditions linked the regeneration environment to SEI-relevant surface speciation and provided a mechanistic basis for selecting regeneration routes to reuse spent graphite as a negative-electrode active material.