Designing a Novel Electrolyte Na3.2 Hf2 Si2.2 P0.8 O11.85 F0.3 for All-Solid-State Na-O2 Batteries

Unraveling the Solvent Effect on Solid-Electrolyte Interphase Formation for Sodium Metal Batteries

Ether-based electrolytes are considered as an ideal electrolyte system for sodium metal batteries (SMBs) due to their superior compatibility with the sodium metal anode (SMA). However, the selection principle of ether solvents and the impact on solid electrolyte interphase formation are still unclear. Herein, we systematically compare the chain ether-based electrolyte and understand the relationship between the solvation structure and the interphasial properties. The linear ether solvent molecules with different terminal group lengths demonstrate remarkably distinct solvation effects, thus leading to different electrochemical performance as well as deposition morphologies for SMBs. Computational calculations and comprehensive characterizations indicate that the terminal group length significantly regulates the electrolyte solvation structure and consequently influences the interfacial reaction mechanism of electrolytes on SMA. Cryogenic electron microscopy clearly reveals the difference in solid electrolyte interphase in various ether-based electrolytes. As a result, the 1,2-diethoxyethane-based electrolyte enables a high Coulombic efficiency of 99.9 %, which also realizes the stable cycling of Na||Na3 V2 (PO4 )3 full cell with a mass loading of ≈9 mg cm-2 over 500 cycles.

Recent progress and strategic perspectives of inorganic solid electrolytes: fundamentals, modifications, and applications in sodium metal batteries

Solid-state electrolytes (SEs) have attracted overwhelming attention as a promising alternative to traditional organic liquid electrolytes (OLEs) for high-energy-density sodium-metal batteries (SMBs), owing to their intrinsic incombustibility, wider electrochemical stability window (ESW), and better thermal stability. Among various kinds of SEs, inorganic solid-state electrolytes (ISEs) stand out because of their high ionic conductivity, excellent oxidative stability, and good mechanical strength, rendering potential utilization in safe and dendrite-free SMBs at room temperature. However, the development of Na-ion ISEs still remains challenging, that a perfect solution has yet to be achieved. Herein, we provide a comprehensive and in-depth inspection of the state-of-the-art ISEs, aiming at revealing the underlying Na⁺ conduction mechanisms at different length scales, and interpreting their compatibility with the Na metal anode from multiple aspects. A thorough material screening will include nearly all ISEs developed to date, i.e., oxides, chalcogenides, halides, antiperovskites, and borohydrides, followed by an overview of the modification strategies for enhancing their ionic conductivity and interfacial compatibility with Na metal, including synthesis, doping and interfacial engineering. By discussing the remaining challenges in ISE research, we propose rational and strategic perspectives that can serve as guidelines for future development of desirable ISEs and practical implementation of high-performance SMBs.

Recent Progress on Honeycomb Layered Oxides as a Durable Cathode Material for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are becoming promising candidates for energy storage devices due to the low cost, abundant reserves, and excellent electrochemical performance. As the most important unit, layered cathodes attract much attention, where honeycomb-layered-oxides (HLOs) manifest outstanding structural stability, high redox potential, and long-life electrochemistry. Here, recent progress on HLOs as well as Na₃ Ni₂ SbO₆ and Na₃ Ni₂ BiO₆ as two representative materials are introduced, and the crystal and electronic structure, electrochemical performance, and modification strategies are summarized. The advanced high nickel HLOs are highlighted toward development of state-of-the-art sodium-ion batteries. This review would deepen the understanding of superstructure in layered oxides, as well as structure-property relationship, and inspire more interest in high output voltage, long lifespan sodium-ion batteries.

Designing a Quasi-Liquid Alloy Interface for Solid Na-Ion Battery

Solid-state sodium-ion batteries are attracting great attention due to their high energy density and high safety. However, the Na dendrite growth and poor wettability between sodium and electrolytes seriously limit its application. Herein, we designed a stable and dendrite-suppressed quasi-liquid alloy interface (C@Na-K) for solid sodium-ion batteries (SSIBs). The batteries exhibit excellent electrochemical performance thanks to better wettability and accelerated charge transfer and nucleation mode shifts. The thickness of the liquid phase alloy interface fluctuates along with the exotherm of the cell cycling process, which leads to better rate performance. The symmetrical cell can cycle steadily over 3500 h at 0.1 mA/cm² at room temperature, and the critical current density can reach 2.6 mA/cm² at 40 °C. The full cells with the quasi-liquid alloy interface also show outstanding performance; the capacity retention can reach 97.1%, and the average Coulombic efficiency can reach 99.6% of the battery at 0.5 C even after 300 cycles. These results proved the feasibility of using a liquid alloy interface of the anode for high-energy SSIBs, and this innovative approach to stabilizing the interface performance could serve as a basis for the development of next-generation high-energy SSIBs.

Organoboron- and Cyano-Grafted Solid Polymer Electrolytes Boost the Cyclability and Safety of High-Voltage Lithium Metal Batteries

Solid-state polymer electrolytes (SPEs) are deemed as a class of sought-after candidates for high-safety and high-energy-density solid-state lithium metal batteries, but their low ionic conductivity, narrow electrochemical windows, and severe interfacial deterioration limit their practical implementations. Herein, an organoboron- and cyano-grafted polymer electrolyte (PVNB) was designed using vinylene carbonate as the polymer backbone and organoboron-modified poly(ethylene glycol) methacrylate and acrylonitrile as the grafted phases, which may facilitate Li-ion transport, immobilize the anions, and enlarge the oxidation voltage window; therefore, the well-tailored PVNB exhibits a high Li-ion transference number (t_Li⁺ = 0.86), a wide electrochemical window (>5 V), and a high ionic conductivity (σ = 9.24 × 10^-4 S cm^-1) at room temperature (RT). As a result, the electrochemical cyclability and safety of the Li|LiFePO₄ and Li|LiNi_0.8Co_0.1Mn_0.1O₂ cells with in situ polymerization of PVNB are substantially improved by forming the stable organic-inorganic composite cathode electrolyte interphase (CEI) and the Li₃N-LiF-rich solid electrolyte interphase (SEI).