Kwang-Sun Ryu

All-solid-state sodium-ion batteries (ASSBs) have emerged as promising next-generation energy storage systems owing to their enhanced safety and thermal stability compared with conventional liquid-electrolyte batteries. Among thiophosphate-based solid electrolytes, Na3PS4 has attracted considerable attention because of its cold-press processability and relatively higher ionic conductivity than oxide-based electrolytes. However, its practical application remains limited by moderate ionic conductivity and poor air stability. In this study, pristine Na3PS4 (NPS) and WO3-substituted Na3PS4 (Na2.9P0.9W0.1S3.7O0.3; NPS-WO-10) solid electrolytes were synthesized through a combination of mechanical milling and low-temperature heat treatment. The substitution of W6+ at the P5+ sites induces sodium vacancies within the cubic Na3PS4 framework, thereby facilitating Na+ ion transport by reducing the migration barrier. The optimized composition, NPS-WO-10 (x = 0.10), exhibited an ionic conductivity of 0.94 mS cm–1 at 30 °C, which is approximately 4.7 times higher than that of pristine Na3PS4 (0.20 mS cm–1). Furthermore, the electronic conductivity remained in the range of 10–6–10–7 S cm–1, indicating its suitability as a solid electrolyte. Moisture stability tests conducted under dry-air conditions (15% relative humidity for 3 h) revealed that WO3 substitution significantly suppressed H2S gas evolution from 16 ppm for pristine NPS to 6 ppm, demonstrating enhanced air stability. An all-solid-state sodium-ion battery employing the NPS-WO-10 electrolyte, Na15Sn4 alloy anode, and NaNi1/3Fe1/3Mn1/3O2 composite cathode delivered an initial discharge capacity of 118 mAh g–1 within the voltage range of 2.3–4.25 V, with an initial Coulombic efficiency of 86.7%. These findings demonstrate that WO3 substitution is an effective strategy for simultaneously enhancing the ionic conductivity and moisture stability of Na3PS4-based solid electrolytes, highlighting their potential for practical ASSB applications.

A series of P2-type layered oxide cathode materials, Na0.67[Mn0.50−x/2Fe0.35−x/2Ni0.15Tix]O2 (x = 0, 0.05, 0.10, and 0.15), hereafter referred to as NFMO and Ti-NFMO, were synthesized via high-energy ball milling followed by calcination at 900°C for 15 h in air. Titanium was introduced as a structural dopant by simultaneously reducing the Mn and Fe site occupancies, thereby preserving charge balance while systematically investigating the influence of Ti4+ incorporation on the structural, morphological, and electrochemical properties of the layered framework. X-ray diffraction (XRD) analysis confirmed that all compositions retained the hexagonal P2-type structure (space group P63/mmc) without detectable secondary phases, indicating the successful solid-solution incorporation of Ti4+ into the transition-metal sublattice. Field-emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) mapping confirmed the homogeneous elemental distribution across all compositions. Electrochemical performance was evaluated in Na-metal half-cells using 1.0 M NaPF6 in propylene carbonate (PC) with 5 wt% fluoroethylene carbonate (FEC) as the electrolyte. The pristine NFMO cathode (x = 0) delivered an initial discharge capacity of 197.6 mAh g−1 at 0.1 C but exhibited severe capacity fade, retaining only 35.7% of its 0.5 C capacity after 50 cycles. By contrast, the optimized Ti-substituted composition (x = 0.15) maintained a high initial discharge capacity of 196.8 mAh g−1 and demonstrated a substantially improved capacity retention of 57.0% after 50 cycles at 0.5 C. Density functional theory (DFT) calculations and SoftBV bond-valence analysis collectively indicate that Ti4+ incorporation modifies the local lattice environment and Na+ migration pathways, while simultaneously suppressing Jahn–Teller-active Mn3+ distortions and adverse phase transitions during repeated cycling. These findings establish Ti substitution as a robust and scalable strategy for enhancing the structural durability and electrochemical cyclability of P2-type layered cathodes for sodium-ion battery applications.

Lithium sulfide (Li ₂ S) is a critical precursor for sulfide-based solid electrolytes in next-generation all-solid-state batteries; accordingly, rigorous control and accurate quantification of trace-level impurities are essential.

Li₂ZrCl₆ 의 이온 전도도를 업그레이드하기 위해 V³⁺ 도핑 을 적용했습니다 . V³⁺ 도핑 은 금속 자리의 Li⁺ 하중 및 전하 균형에 영향을 미쳐 전도도를 끌어올리는 것으로 예상됩니다. V 도핑된 Li₂ZrCl₆ 는 고 에너지 볼 밀링 법으로 합성 변환, X선 회절, 라만 분광법 및 X선 광전자 분광법을 이용하여 구조적 대칭을 분석했습니다. 전기화 성능은 전기화학적 논리적 분광법, 순환 전압 흐름법 및 정전류 충방전 측정을 통해 평가되었습니다. 제네 Li₂ZrCl₆와 비교했을 때 , V 도핑 (x = 0.1) Li₂ZrCl₆ 의 전도도는 0.41 mS/cm에서 0.70 mS/cm로 증가했고, 활성화 에너지는 0.345 eV에서 0.318 eV로 되었습니다 . 이러한 결과는 V 도핑 이 Li₂ZrCl₆ 의 활성화 에너지를 억제어 Li⁺온의 이동성을 감소시킬 수 있음을 보여줍니다. 또한, 정흐름 충방전 측정 결과 100회 주기 동안 캡슐 유지율이 13% 향상된 결과를 얻었습니다. 100회 충방전 추가 후 Li₂₁Zr₀.₉V₀.₁Cl₆의 총 저항은 순수 Li₂ZrCl₆ 보다 느리게 하고 , 그리고 V 도핑 이 더욱 내부 작동 중 저항을 계속하고 전고체 배터리에 등록하는 것을 향상시키는 것을 나타냅니다.