Hong Chen

Chloride‐ion batteries (CIBs) represent a promising post‐lithium energy storage platform combining high theoretical energy density with elemental sustainability. However, All‐Solid‐State CIBs (ASS‐CIBs) remain hindered by limited ionic transport and interfacial instability. Here, we demonstrate a high‐performance VOCl/CsSn ₀ . ₉ In ₀ . ₀₆₇ Cl ₃ (CSIC)/In system wherein systematic optimization of the cathode composite identifies an optimal 30:60:10 (VOCl/CSIC/C) ratio, delivering an initial specific capacity of 169 mAh g ^{− 1} . X‐ray diffraction (XRD) with Rietveld refinement and field‐emission scanning electron microscopy (FESEM) confirmed phase purity and uniform particle distribution, while increasing stack pressure from 130 to 400 MPa markedly enhanced interfacial contact and active material utilization. The optimized configuration sustained stable cycling over 500 cycles at 0.1 mA cm ^{− 2} with nearly 100% Coulombic efficiency. Time‐resolved electrochemical impedance spectroscopy (EIS), analyzed using the distribution of relaxation times (DRT) method, identified the VOCl–CSIC cathode interface as the dominant resistance contributor, while the In–CSIC anode remained comparatively stable. Ex situ XRD and focused ion beam–scanning electron microscopy (FIB‐SEM) corroborated these findings, revealing reversible phase transitions alongside structural breathing, particle cracking, and void formation. This work provides a kinetically and structurally rationalized design strategy toward durable ASS‐anionic shuttle batteries based on powdered electrode architectures.

This study probes stack-pressure effects in ASSFIBs with BiF ₃ |BaSnF ₄ |Sn cells. A high 180 MPa boosts cycling by improving F ⁻ transport, mitigating oxygen-related interfacial degradation and stabilizing phase evolution of BiF ₃ cathodes.

Magnesium spinels such as MgAl₂O₄ and MgFe₂O₄ have been widely explored for energy storage and sensing applications, but MgV₂O₄ remains relatively unexplored despite its promising potential, e.g., as a battery electrode material. In this study, we report the first mechanochemical synthesis of MgV₂O₄ at room temperature using either MgO or Mg with various vanadium oxides as reactants. Directed by thermodynamic calculations on a DFT level, only the self-sustaining reaction between V₂O₅ and Mg led to MgV₂O₄ within 20 min of milling, along with MgO as a side product. With increasing rotational speed, an earlier reaction ignition after a few minutes of milling, smaller crystallite sizes in the nanometer range, and increased strain in MgV₂O₄ were observed. In addition, harsh milling conditions induce increasing nonstoichiometry in both phases, leading to a magnesium-rich spinel and a vanadium-containing rock salt phase, as supported by X-ray diffraction and electron paramagnetic resonance measurements. Acid washing after synthesis removed MgO, and electrochemical impedance spectroscopy showed that milder grinding conditions increased the conductivity of MgV₂O₄ due to the smaller number of defects.

Among all the alternative battery systems beyond lithium-ion batteries (LIBs), all-solid-state fluoride ion batteries (ASSFIBs) are particularly promising due to their high theoretical energy density, thermal stability, and recent advancements in room-temperature superionic solid electrolytes and intercalation-type electrodes. However, their practical application is hindered by poor cycling stability and limited rate capability, largely attributed to unfavored kinetics and interfacial degradation, especially in conversion-type cathodes. Previous studies have shown that the application of stack pressure can significantly improve the cell’s cycling stability. To reveal the underlying mechanism, this study systematically investigates the impact of stack pressure on the electrochemical performance of ASSFIBs using BiF₃|BaSnF₄|Sn cells. Among the tested conditions, the best enhancement of cycling stability and rate performance were demonstrated under 180 MPa. Furthermore, ex-situ diffraction analysis revealed pressure-dependent phase evolution and oxygen-related interfacial degradation (i.e., BiOF or BiO0.1O2.8 formation) in the BiF₃ cathode during the first cycle. Through in-situ electrochemical impedance spectroscopy combined with distribution of relaxation times analysis we identified charge transfer and F⁻ diffusion as the dominant state-of-charge dependent kinetic limitations, with strong correlation to phase transitions within the BiF₃ cathode composite. These findings emphasize the critical role of stack pressure in mitigating interfacial degradation and optimizing ion transport, providing valuable insights for the design and operation of high-performance ASSFIBs.

To improve the performance of high‐energy‐density electrode materials for all‐solid‐state fluoride‐ion batteries (ASSFIBs), it is important to understand the structure and phase evolution during operation, which is closely correlated to capacity fading. In this study, an operando cell is designed compatible with laboratory X‐ray diffraction (XRD) to monitor real‐time structural changes of bismuth trifluoride (BiF ₃ ) cathodes and degradation of the ionic conductor BaSnF ₄ under negative potentials at 100 °C. Supported by ex‐situ XRD, our results reveal a multi‐step defluorination of BiF ₃ : from orthorhombic (o‐BiF ₃ ) to cubic (c‐BiF ₃ ), then to distorted orthorhombic (o’‐BiF ₃ ), and finally to metallic bismuth (Bi), indicating partial intercalation‐type character. Formation of bismuth oxidefluoride (BiOF) beyond 200 mAh g ⁻¹ is attributed to oxygen impurities introduced via solid‐state synthesis. operando X‐ray absorption spectroscopy (XAS) confirms a continuous reduction of Bi ₃₊ to Bi ₀ with intermediate phases. Rietveld refinement quantifies the phase fractions and structural transitions, enabling a model for BiF ₃ defluorination. Comparison of operando XRD and XAS reveals that BaSnF ₄ contributes transport of both fluoride and oxygen impurities, leading to BiOF formation. BaSnF ₄ also exhibits a broad stability window, with degradation occurring below −200 mV, rather than the expected −50 mV vs. Sn/SnF ₂ .

To rationalize and improve the performance of high energy density electrode materials for all-solid-state fluoride ion batteries and abstract the increasing demands of energy storage, it is important to gain a fundamental understanding of structure/phase evolution during cell operation, which is closely correlated to capacity fading upon cycling. Here, we design an operando cell for laboratory X-ray diffraction, by which we monitor the real-time structure evolution of BiF3 cathode materials and the degradation of superior ionic conductor BaSnF4 over the negative cell potential range against Sn/SnF2 anode at an elevated temperature (100 °C). The results, together with ex-situ XRD measurements, reveal that BiF3 undergoes multiple-step phase transformations upon defluorination (from original o-BiF3 to c-BiF3 and then o’-BiF3) before the formation of Bi metal, showing an intercalation-type mechanism. In addition, the formation of Bismuth oxidefluoride (BiOF) at later discharged state (beyond a capacity of 200 mAh g-1) is observed, which is attributed to oxygen impurities from the solid electrolyte introduced by the applied solid state synthesis method. Operando XAS measurements confirm the continuous reduction of the Bi oxidation state from +3 to 0 and the formation of multi-intermediate phases during the defluorination process. Through Rietveld analysis on operando XRD patterns we obtain the quantification of phase fractions and crystal structure information of intermediate phases during the defluorination process, from which we are able to derive a model for the first defluorination process of BiF3 at elevated temperatures. Furthermore, the comparison between the results from operando XAS and operando XRD indicates that BaSnF4 plays a crucial role on the transport process of not only F- but also oxygen impurities within the BiF3 cathode composite, contributing to the formation of the oxidefluoride phase. In addition, BaSnF4 shows a rather wide potential window, with degradation taking place at a potential below -200 mV (against Sn/SnF2 anode).

If all‐solid‐state fluoride‐ion batteries want to compete with existing battery technologies, significant improvements in terms of cyclic stability are necessary to fully access the high specific capacities, which this battery concept can provide in theory. Herein, the development of a high‐pressure, high‐temperature battery operation stand for battery cycling under inert conditions inside a glovebox is reported. This stand is then used to investigate the effect of stack pressure on the cell performance of conversion‐based as well as intercalation‐based electrode materials for fluoride‐ion batteries. It is found that cyclic stability as well as energy efficiency is strongly increased compared to nonpressure conditions, which is assigned to sustained interparticle contact. Thus, the cell design must be considered carefully to be able to distinguish intrinsic material properties from percolation‐ and interphase‐related impacts on the cell behavior. Further, the effect of pressure on the ionic conductivity of common solid fluoride‐ion conductors is investigated.