Long Cycle Life All-Solid-State Sodium Ion Battery

Accumulative Delocalized Mo 4d Electrons to Bound the Volume Expansion and Accelerate Kinetics in Mo6S8 Cathode for High-Performance Aqueous Cu2+ Storage

Electronic structure defines the conductivity and ion absorption characteristics of a functional electrode, significantly affecting the charge transfer capability in batteries, while it is rarely thought to be involved in mesoscopic volume and diffusion kinetics of the host lattice for promoting ion storage. Here, we first correlate the evolution in electronic structure of the Mo6S8 cathode with the ability to bound volume expansion and accelerate diffusion kinetics for high-performance aqueous Cu2+ storage. Operando synchrotron energy-dispersive X-ray absorption spectroscopy reveals that accumulative delocalized Mo 4d electrons enhance the Mo-Mo interaction with distinctly contracting and uniformizing Mo6 clusters during the reduction of Mo6S8, which potently restrain lattice expansion and release space to promote Cu2+ diffusion kinetics. Operando synchrotron X-ray diffraction and comprehensive characterizations further validate the structural and electrochemical properties induced by the Cu2+ intercalation electronic structure, endowing the Mo6S8 cathode a high specific capacity with small volume expansion, fast ions diffusion, and long-term cycling stability.

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.

Insight into the structural and electrochemical properties of the interface between a Na6SOI2 solid electrolyte and a metallic Na anode

Solid electrolytes (SE) have attracted a great deal of interest as they can not only mitigate the safety issues related to currently used liquid organic electrolytes but also enable the introduction of a metallic Na anode with extreme energy density in sodium-ion batteries. For such application, SE should exhibit high interfacial stability against metallic Na as well as high ionic conductivity, and Na₆SOI₂ with a Na-rich double anti-perovskite structure was recently identified as a promising SE candidate. In this work, we performed first principles calculations to investigate the structural and electrochemical properties of the interface between Na₆SOI₂ and a metallic Na anode. Our calculations revealed that interfaces could be formed safely, keeping the ultra-fast ionic conductivity of the bulk phase near the interface. Through the electronic structure analysis of the interface models, we found the change of upward valence band bending at the surface to downward band bending at the interface, being accompanied by electronic charge transfer from a metallic Na anode to Na₆SOI₂ SE at the interface. This work provides valuable atomistic insight into the formation and properties of the interface between SE and alkali metal for enhancing battery performance.

Metallic Sodium Anodes for Advanced Sodium Metal Batteries: Progress, Challenges and Perspective

Sodium (Na)-based batteries, as the ideal choice of large-scale and low-cost energy storage, have attracted much attention. Na metal anodes with high theoretical specific capacity and low potential are considered to be one of the most promising anodes for next-generation Na-based batteries. However, the high reactivity of Na metal anodes makes the electrode/electrolyte phase unstable, resulting in formation of Na dendrites, short cycle life and safety problems. Herein, the contribution outlines the latest development of Na metal anodes for Na metal batteries. The design strategies for high efficiency utilization of Na metal anodes are elucidated, including sophisticated electrode construction, liquid electrolyte optimization, electrode/electrolyte interface stabilization, and solid electrolyte adaptation. Finally, the future research direction and existing problems are proposed.

Stable Quasi-Solid-State Aluminum Batteries

Nonaqueous rechargeable aluminum batteries (RABs) of low cost and high safety are promising for next-generation energy storage. With the presence of ionic liquid (IL) electrolytes, their high moisture sensitivity and poor stability would lead to critical issues in liquid RABs, including undesirable gas production, irreversible activity loss, and an unstable electrode interface, undermining the operation stability. To address such issues, herein, a stable quasi-solid-state electrolyte is developed via encapsulating a small amount of an IL into a metal-organic framework, which not only protects the IL from moisture, but creates sufficient ionic transport network between the active materials and the electrolyte. Owing to the generated stable states at both positive-electrode-electrolyte and negative-electrode-electrolyte interfaces, the as-assembled quasi-solid-state Al-graphite batteries deliver specific capacity of ≈75 mA h g^-1 (with positive electrode material loading ≈9 mg cm^-2 , much higher than that in the conventional liquid systems). The batteries present a long-term cycling stability beyond 2000 cycles, with great stability even upon exposure to air within 2 h and under flame combustion tests. Such technology opens a new platform of designing highly safe rechargeable Al batteries for stable energy storage.

Computational Auxiliary for the Progress of Sodium-Ion Solid-State Electrolytes

All-solid-state sodium batteries (ASSBs) have attracted ever-increasing attention due to their enhanced safety, high energy density, and the abundance of raw materials. One of the remaining key issues for the practical ASSB is the lack of good superionic and electrochemical stable solid-state electrolytes (SEs). Design and manufacturing specific functional materials used as high-performance SEs require an in-depth understanding of the transport mechanisms and electrochemical properties of fast sodium-ion conductors on an atomic level. On account of the continuous progress and development of computing and programming techniques, the advanced computational tools provide a powerful and convenient approach to exploit particular functional materials to achieve that aim. Herein, this review primarily focuses on the advanced computational methods and ion migration mechanisms of SEs. Second, we overview the recent progress on state-of-the-art solid sodium-ion conductors, including Na-β-alumina, sulfide-type, NASICON-type, and antiperovskite-type sodium-ion SEs. Finally, we outline the current challenges and future opportunities. Particularly, this review highlights the contributions of the computational studies and their complementarity with experiments in accelerating the study progress of high-performance sodium-ion SEs for ASSBs.

Interfacial processes in electrochemical energy systems

Electrochemical energy systems such as batteries, water electrolyzers, and fuel cells are considered as promising and sustainable energy storage and conversion devices due to their high energy densities and zero or negative carbon dioxide emission. However, their widespread applications are hindered by many technical challenges, such as the low efficiency and poor long-term cyclability, which are mostly affected by the changes at the reactant/electrode/electrolyte interfaces. These interfacial processes involve ion/electron transfer, molecular/ion adsorption/desorption, and complex interface restructuring, which lead to irreversible modifications to the electrodes and the electrolyte. The understanding of these interfacial processes is thus crucial to provide strategies for solving those problems. In this review, we will discuss different interfacial processes at three representative interfaces, namely, solid-gas, solid-liquid, and solid-solid, in various electrochemical energy systems, and how they could influence the performance of electrochemical systems.

Insights into the Rich Polymorphism of the Na+ Ion Conductor Na3PS4 from the Perspective of Variable-Temperature Diffraction and Spectroscopy

Solid electrolytes are crucial for next-generation solid-state batteries, and Na₃PS₄ is one of the most promising Na⁺ conductors for such applications, despite outstanding questions regarding its structural polymorphs. In this contribution, we present a detailed investigation of the evolution in structure and dynamics of Na₃PS₄ over a wide temperature range 30 < T < 600 °C through combined experimental-computational analysis. Although Bragg diffraction experiments indicate a second-order phase transition from the tetragonal ground state (α, P4̅2₁ c) to the cubic polymorph (β, I4̅3m) above ∼250 °C, pair distribution function analysis in real space and Raman spectroscopy indicate remnants of a tetragonal character in the range 250 < T < 500 °C, which we attribute to dynamic local tetragonal distortions. The first-order phase transition to the mesophasic high-temperature polymorph (γ, Fddd) is associated with a sharp volume increase and the onset of liquid-like dynamics for sodium-cations (translational) and thiophosphate-polyanions (rotational) evident by inelastic neutron and Raman spectroscopies, as well as pair-distribution function and molecular dynamics analyses. These results shed light on the rich polymorphism of Na₃PS₄ and are relevant for a range host of high-performance materials deriving from the Na₃PS₄ structural archetype.

Stabilization of Li0.33La0.55TiO3 Solid Electrolyte Interphase Layer and Enhancement of Cycling Performance of LiNi0.5Co0.3Mn0.2O2 Battery Cathode with Buffer Layer

All-solid-state batteries (ASSBs) are attractive for energy storage, mainly because introducing solid-state electrolytes significantly improves the battery performance in terms of safety, energy density, process compatibility, etc., compared with liquid electrolytes. However, the ionic conductivity of the solid-state electrolyte and the interface between the electrolyte and the electrode are two key factors that limit the performance of ASSBs. In this work, we investigated the structure of a Li0.33La0.55TiO3 (LLTO) thin-film solid electrolyte and the influence of different interfaces between LLTO electrolytes and electrodes on battery performance. The maximum ionic conductivity of the LLTO was 7.78 × 10-5 S/cm. Introducing a buffer layer could drastically improve the battery charging and discharging performance and cycle stability. Amorphous SiO2 allowed good physical contact with the electrode and the electrolyte, reduced the interface resistance, and improved the rate characteristics of the battery. The battery with the optimized interface could achieve 30C current output, and its capacity was 27.7% of the initial state after 1000 cycles. We achieved excellent performance and high stability by applying the dense amorphous SiO2 buffer layer, which indicates a promising strategy for the development of ASSBs.

Elastic NaxMoS2-Carbon-BASE Triple Interface Direct Robust Solid-Solid Interface for All-Solid-State Na-S Batteries

The developments of all-solid-state sodium batteries are severely constrained by poor Na-ion transport across incompatible solid-solid interfaces. We demonstrate here a triple Na_xMoS₂-carbon-BASE nanojunction interface strategy to address this challenge using the β″-Al₂O₃ solid electrolyte (BASE). Such an interface was constructed by adhering ternary Na electrodes containing 3 wt % MoS₂ and 3 wt % carbon on BASE and reducing contact angles of molten Na to ∼45°. The ternary Na electrodes exhibited twice improved elasticity for flexible deformation and intimate solid contact, whereas Na_xMoS₂ and carbon synergistically provide durable ionic/electronic diffusion paths, which effectively resist premature interface failure due to loss of contact and improved Na stripping utilization to over 90%. Na metal hosted via triple junctions exhibited much smaller charge-transfer resistance and 200 h of stable cycling. The novel interface architecture enabled 1100 mAh/g cycling of all-solid-state Na-S batteries when using advanced sulfur cathodes with Na-ion conductive PEO₁₀-NaFSI binder and Na_xMo₆S₈ redox catalytic mediator.

Yttrium-Sodium Halides as Promising Solid-State Electrolytes with High Ionic Conductivity and Stability for Na-Ion Batteries

All-solid-state sodium-ion batteries (ASIBs) are promising candidates for large-scale energy storage applications. To build such a battery system, efficient solid-state electrolytes (SSEs) with high sodium ionic conductivity at room temperature and good electrochemical stability as well as interface compatibility are required. In this work, using density functional theory combined with molecular dynamics simulation and a phase diagram, we have studied the potential of yttrium halide-based materials (Na₃YX₆, where X = Cl or Br) with inherent cation vacancies as diffusion carriers for solid electrolytes in ASIBs. A great balance between electrochemical stability and ionic conductivity found in these two systems overcomes the shortcomings of sulfide- and oxide-based SSEs. In particular, these two materials show Na⁺ conductivities of 0.77 and 0.44 mS cm^-1 at 300 K and wide electrochemical windows of 0.51-3.75 and 0.57-3.36 V, and good interfacial stability with Na metal anode and high-potential polyanion (fluoro)phosphate cathode materials, respectively. These features make halide-based materials promising efficient solid-state electrolytes for Na-ion batteries.

Material and Interfacial Modification toward a Stable Room-Temperature Solid-State Na-S Battery

Room-temperature solid-state sodium batteries have the remarkable potential to simultaneously achieve high safety, high energy density, and low cost. However, their current performance is far below expectations. Through material and interfacial modification based on Na₃PS₄ solid electrolytes, progress is made toward stable room-temperature solid-state sodium-sulfur (Na-S) batteries. First, the ionic liquid N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (Pyr₁₄FSI) is employed to modify the anode/electrolyte interface. An overpotential of 0.55 V after 900 h of a symmetrical battery indicates enhanced interfacial stability. A stable in situ solid electrolyte interphase layer is formed at the interface of NaSn alloy and Na₃PS₄, proved by X-ray photoelectron spectroscopy measurements. Furthermore, selenium-doped sulfurized polyacrylonitrile (Se_0.05S_0.95@pPAN) is used to boost the ionic and electronic conductivities of the sulfur cathode. As a result, the Na-S battery using a Se_0.05S_0.95@pPAN cathode and the interfacial modification delivers stable cycle performance and enhanced rate capability.

Iodine Vapor Transport-Triggered Preferential Growth of Chevrel Mo6S8 Nanosheets for Advanced Multivalent Batteries

Owing to its unique structure, Chevrel phase (CP) is a promising candidate for applications in rechargeable multivalent (Mg and Al) batteries. However, its wide applications are severely limited by time-consuming and complex synthesis processes, accompanied by uncontrollable growth and large particle sizes, which will magnify the charge trapping effect and lower the electrochemical performance. Here, an iodine vapor transport reaction (IVT) is proposed to obtain large-scale and highly pure Mo₆S₈ nanosheets, in which iodine helps to regulate the growth kinetics and induce the preferential growth of Mo₆S₈, as a typical three-dimensional material, to form nanosheets. When applied in rechargeable multivalent (Mg and Al) batteries, Mo₆S₈ nanosheets show very fast kinetics owing to the short diffusion distance, thereby exhibiting lower polarization, higher capacities, and better low-temperature performance (up to -40 °C) compared to that of microparticles obtained via the conventional method. It is anticipated that Mo₆S₈ nanosheets would boost the application of Chevrel phase, especially in areas of energy storage and catalysis, and the IVT reaction would be generalized to a wide range of inorganic compound nanosheets.