Recent advances in solid-state beyond lithium batteries

Exploring Li2MgZrO4 as a multifunctional material: structural analysis, polaron conductivity, and wide bandgap for energy and optoelectronic devices

The search for advanced materials with tunable electronic and optical properties has driven significant progress in energy storage and optoelectronic technology. Lithium-based mixed-metal oxides stand out among these materials because of their excellent ionic conductivity and structural flexibility. This study focuses on examining the structural, electrical, and optical characteristics of Li2MgZrO4, a ternary oxide featuring a tetragonal layered structure (space group P42/nmc). The material was prepared using a solid-state synthesis method and its single-phase nature was validated by X-ray diffraction analysis combined with Rietveld refinement. Additionally, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were employed to evaluate the microstructural features and elemental distributions of the compounds. UV-vis-NIR spectroscopy revealed a direct bandgap of 3.41 eV, highlighting the material's potential for optoelectronic applications. Impedance spectroscopy studies demonstrated a non-Debye relaxation behavior and thermally activated conductivity. Examination of AC conductivity using Jonscher's power law and the overlapping large polaron tunneling (OLPT) model revealed that polaronic conduction mechanisms primarily govern charge transport. The activation energy (0.804 eV) further supported thermally activated conduction. These results highlight Li2MgZrO4 as a multifunctional material with considerable potential for applications in solid-state battery design, energy storage systems, and optoelectronic innovations.

Status and Challenges of Solid-State Electrolytes for Potassium Batteries

Potassium solid-state batteries (K-SSBs), utilizing solid-state K-ion electrolytes (K-SSEs) and potassium metal anodes, are promising candidates for large-scale energy storage due to their low cost, safety, and high energy density. The limited availability of K-SSEs with excellent electrochemical performances and the associated interfacial issues are the primary hurdles in advancing K-SSBs. In this review, the ion conduction mechanism and the key parameters of solid electrolytes are re-examined, and then reviewed typical inorganic and polymer electrolytes for K-ion migration, highlighting the critical role of electrolyte crystal structure, composition, and preparation techniques in achieving optimal ionic conductivity and stability. This study further emphasizes the essential role of strategic interface engineering, including the formation of stable solid-electrolyte interphases at the anode and the construction of efficient K⁺-ion transport channels at the cathode, on mitigating interfacial impedance and enabling stable cycling performance of K-SSBs. Finally, promising research directions are proposed to advance the development of high-performance K-SSEs, anticipating to provide some inspiration and reference for the continued advancement of K-SSBs.

Exploration of Chemical Space Through Automated Reasoning

The vast size of composition space poses a significant challenge for materials chemistry: exhaustive enumeration of potentially interesting compositions is typically infeasible, hindering assessment of important criteria ranging from novelty and stability to cost and performance. We report a tool, Comgen, for the efficient exploration of composition space, which makes use of logical methods from computer science used for proving theorems. We demonstrate how these techniques, which have not previously been applied to materials discovery, can enable reasoning about scientific domain knowledge provided by human experts. Comgen accepts a variety of user-specified criteria, converts these into an abstract form, and utilises a powerful automated reasoning algorithm to identify compositions that satisfy these user requirements, or prove that the requirements cannot be simultaneously satisfied. In contrast to machine learning techniques, explicitly reasoning about domain knowledge, rather than making inferences from data, ensures that Comgen's outputs are fully interpretable and provably correct. Users interact with Comgen through a high-level Python interface. We illustrate use of the tool with several case studies focused on the search for new ionic conductors. Further, we demonstrate the integration of Comgen into an end-to-end automated workflow to propose and evaluate candidate compositions quantitatively, prior to experimental investigation. This highlights the potential of automated formal reasoning in materials chemistry.

Single Na- and K-Ion-Conducting Sulfonated -NH-Linked Covalent Organic Frameworks

Highly ion-conductive solid electrolytes of nonlithium ions (sodium or potassium ions) are necessary for pursuing a more cost-effective and sustainable energy storage. Here, two classes of sulfonated -NH-linked covalent organic frameworks (COFs), specifically designed for sodium or potassium ion conduction (named i-COF-2 (Na or K) and i-COF-3 (Na or K)), were synthesized through a straightforward, one-step process using affordable starting materials. Remarkably, these COFs demonstrate high ionic conductivity at room temperature─3.17 × 10-4 and 1.02 × 10-4 S cm-1 for i-COF-2 (Na) and i-COF-2 (K) and 2.75 × 10-4 and 1.42 × 10-4 S cm-1 for i-COF-3 (Na) and i-COF-3 (K)─without the need for additional salt or solvent. This enhanced performance, including low activation energies of 0.21 eV for both i-COF-2 (Na) and i-COF-2 (K) and of 0.24 and 0.25 eV for i-COF-3 (Na) and i-COF-3 (K), is attributed to the strategic incorporation of sulfonate groups and the directional channels within the COF structure. The Na+ and K+ ion high conductivities, low cost, and intrinsic framework stability of i-COF-2 (Na or K) and i-COF-3 (Na or K) provide promising solid electrolyte candidates for the exploration of sustainable energy storage.

Advances in Electrochemical Energy Storage over Metallic Bismuth-Based Materials

Bismuth (Bi) has been prompted many investigations into the development of next-generation energy storage systems on account of its unique physicochemical properties. Although there are still some challenges, the application of metallic Bi-based materials in the field of energy storage still has good prospects. Herein, we systematically review the application and development of metallic Bi-based anode in lithium ion batteries and beyond-lithium ion batteries. The reaction mechanism, modification methodologies and their relationship with electrochemical performance are discussed in detail. Additionally, owing to the unique physicochemical properties of Bi and Bi-based alloys, some innovative investigations of metallic Bi-based materials in alkali metal anode modification and sulfur cathodes are systematically summarized for the first time. Following the obtained insights, the main unsolved challenges and research directions are pointed out on the research trend and potential applications of the Bi-based materials in various energy storage fields in the future.

Reference Electrode Reveals Insights on Sodium Metal/Solid Electrolyte Interface Cycling and Voiding Behaviors at High Current Densities and Areal Capacities

Plating and stripping processes at solid metal electrode/solid electrolyte interfaces are of great significance for high-energy, solid-state batteries. Here, we introduce a Na metal reference electrode to a symmetric Na metal/sodium β″ alumina/Na metal cell and study both cycling and unidirectional protocols with a focus on high current density and areal capacity. For example, in a current ramp test at 5 mAh cm-2 we find a shift from stable to unstable interfacial polarization during stripping at ≳3 mA cm-2, and at 7.5 mA cm-2 we measure 100s of mV of voltage magnitude rise at the stripping electrode and 10s of mV of voltage changes at the plating electrode. In unidirectional testing (i.e., passing current in a single direction until cell failure), at 1.2 mA cm-2 we find only ∼40% of the initial Na foil could be transferred through the solid electrolyte and again observe 100s of mV (and larger) voltage magnitude rise at the stripping electrode and 10s of mV of voltage change at the plating electrode. This test also shows that the 100s of mV of interfacial polarization can be sustained for hours (at 1.2 mA cm-2) to tens of hours (in a test at 0.3 mA cm-2). Hence, across several test protocols we find a Na metal reference electrode provides quantitative insights on electrochemical interfacial behavior that are not revealed in two-electrode testing. We also built a two-dimensional model of our three-electrode symmetric cell to quantify the link between the measured interfacial potentials in our testing and changes in electrochemically active interfacial contact and find that 100s of mV of interfacial potential rise indicates loss of electrochemically active contact area of >80%. Our work provides a promising approach to clarify the coupled interfacial electrochemical and contact mechanics processes at solid metal electrode/solid electrolyte interfaces.