Research Progress toward Room Temperature Sodium Sulfur Batteries: A Review

Role of inorganic layers on polysulfide decomposition at sodium-metal anode surfaces for room temperature Na/S batteries

Sodium metal is a promising anode material for room-temperature sodium sulfur batteries. Due to its high reactivity, typical liquid electrolytes (e.g. carbonate-based solvents and a Na salt) can undergo reduction to form a solid electrolyte interphase (SEI) layer, with inorganic components such as Na2CO3, Na2O, and NaOH, covering the anode surface along with other SEI organic products. One of the challenges is to understand the effect of the SEI film on the decomposition of soluble sodium polysulfide molecules (e.g., Na2S8) upon shuttling from the cathode to anode during battery cycling. Here, we use ab initio molecular dynamics (AIMD) simulations to study the role of an inorganic SEI used as a model passivation layer in polysulfide decomposition. Compared to other film chemistries, it is found that the Na2CO3 film can suppress decomposition with the slowest reduction rate and the smallest amount of charge transfer towards Na2S8. The Na2CO3 film can maintain its structural properties during the simulations. In contrast, Na2O and NaOH allow some decomposed polysulfide fragments to be inserted into the SEI layer. Moreover, the decomposition of Na2S8 on both Na2O and NaOH SEI layers is more reactive with more charge transfer to Na2S8 when compared to that of Na2CO3. Thus, the ability of the SEI to suppress polysulfide decomposition is in the order: Na2CO3 > NaOH ∼ Na2O. Analyses of the density of states reveal that the Na2S8 molecule receives electrons from the Na metal directly in the presence of n-type semiconductor films of Na2CO3 and NaOH, while the charge migration behavior is different in a p-type semiconductor Na2O with the SEI film donating its electrons to the polysulfide solely. Thus, this work adds new insights into charge transfer behavior of inorganic thin film SEIs that could be present at the initial stages of SEI formation.

Research on Wide-Temperature Rechargeable Sodium-Sulfur Batteries: Features, Challenges and Solutions

Sodium-sulfur (Na-S) batteries hold great promise for cutting-edge fields due to their high specific capacity, high energy density and high efficiency of charge and discharge. However, Na-S batteries operating at different temperatures possess a particular reaction mechanism; scrutinizing the optimized working conditions toward enhanced intrinsic activity is highly desirable while facing daunting challenges. This review will conduct a dialectical comparative analysis of Na-S batteries. Due to its performance, there are challenges in the aspects of expenditure, potential safety hazards, environmental issues, service life and shuttle effect; thus, we seek solutions in the electrolyte system, catalysts, anode and cathode materials at intermediate and low temperatures (T < 300 °C) as well as high temperatures (300 °C < T < 350 °C). Nevertheless, we also analyze the latest research progress of these two situations in connection with the concept of sustainable development. Finally, the development prospects of this field are summarized and discussed to look forward to the future of Na-S batteries.

A Multifunctional Coating on Sulfur-Containing Carbon-Based Anode for High-Performance Sodium-Ion Batteries

A sulfur doping strategy has been frequently used to improve the sodium storage specific capacity and rate capacity of hard carbon. However, some hard carbon materials have difficulty in preventing the shuttling effect of electrochemical products of sulfur molecules stored in the porous structure of hard carbon, resulting in the poor cycling stability of electrode materials. Here, a multifunctional coating is introduced to comprehensively improve the sodium storage performance of a sulfur-containing carbon-based anode. The physical barrier effect and chemical anchoring effect contributed by the abundant C-S/C-N polarized covalent bond of the N, S-codoped coating (NSC) combine to protect SGCS@NSC from the shuttling effect of soluble polysulfide intermediates. Additionally, the NSC layer can encapsulate the highly dispersed carbon spheres inside a cross-linked three-dimensional conductive network, improving the electrochemical kinetic of the SGCS@NSC electrode. Benefiting from the multifunctional coating, SGCS@NSC exhibits a high capacity of 609 mAh g^-1 at 0.1 A g^-1 and 249 mAh g^-1 at 6.4 A g^-1. Furthermore, the capacity retention of SGCS@NSC is 17.6% higher than that of the uncoated one after 200 cycles at 0.5 A g^-1.

Progress and Prospect of Zn Anode Modification in Aqueous Zinc-Ion Batteries: Experimental and Theoretical Aspects

Aqueous zinc-ion batteries (AZIBs), the favorite of next-generation energy storage devices, are popular among researchers owing to their environmental friendliness, low cost, and safety. However, AZIBs still face problems of low cathode capacity, fast attenuation, slow ion migration rate, and irregular dendrite growth on anodes. In recent years, many researchers have focused on Zn anode modification to restrain dendrite growth. This review introduces the energy storage mechanism and current challenges of AZIBs, and then some modifying strategies for zinc anodes are elucidated from the perspectives of experiments and theoretical calculations. From the experimental point of view, the modification strategy is mainly to construct a dense artificial interface layer or porous framework on the anode surface, with some research teams directly using zinc alloys as anodes. On the other hand, theoretical research is mainly based on adsorption energy, differential charge density, and molecular dynamics. Finally, this paper summarizes the research progress on AZIBs and puts forward some prospects.

Polysulfide Catalytic Materials for Fast-Kinetic Metal-Sulfur Batteries: Principles and Active Centers

Benefiting from the merits of low cost, ultrahigh-energy densities, and environmentally friendliness, metal-sulfur batteries (M-S batteries) have drawn massive attention recently. However, their practical utilization is impeded by the shuttle effect and slow redox process of polysulfide. To solve these problems, enormous creative approaches have been employed to engineer new electrocatalytic materials to relieve the shuttle effect and promote the catalytic kinetics of polysulfides. In this review, recent advances on designing principles and active centers for polysulfide catalytic materials are systematically summarized. At first, the currently reported chemistries and mechanisms for the catalytic conversion of polysulfides are presented in detail. Subsequently, the rational design of polysulfide catalytic materials from catalytic polymers and frameworks to active sites loaded carbons for polysulfide catalysis to accelerate the reaction kinetics is comprehensively discussed. Current breakthroughs are highlighted and directions to guide future primary challenges, perspectives, and innovations are identified. Computational methods serve an ever-increasing part in pushing forward the active center design. In summary, a cutting-edge understanding to engineer different polysulfide catalysts is provided, and both experimental and theoretical guidance for optimizing future M-S batteries and many related battery systems are offered.

A Monolithic Solid-State Sodium-Sulfur Battery with Al-Doped Na3.4Zr2(Si0.8P0.2O4)3 Electrolyte

The limit of the energy density and increasing security issues on sodium-ion batteries (SIBs) impede their further development. Solid-state sodium metal batteries are potential candidates to replace the present SIBs. However, low ionic conductivity and poor interface contact hinder their progress. In this work, the impact of Al doping on the crystalline structure and ionic transport in Na_3.4Zr₂(Si_0.8P_0.2O₄)₃ was studied by neutron powder diffraction. The ionic conductivity of Na_3.5Zr_1.9Al_0.1Si_2.4P_0.6O₁₂ achieves 4.43 × 10^-3 S cm^-1 at 50 °C. The polarization voltage of the Na||Na symmetric battery is about 40 mV after cycling for more than 1600 h. Moreover, a solid-state sodium-sulfur battery with a monolithic structure was constructed to alleviate the interfacial resistance problems. Its specific discharge capacity can still keep 300 mA h g^-1 after 480 cycles at 300 mA g^-1. The work provides a promising strategy to design solid-state sodium-sulfur batteries with high performances.

Recent Advances of Catalytic Effects in Cathode Materials for Room-Temperature Sodium-Sulfur Batteries

Electrocatalysts in room-temperature sodium-sulfur (RT-Na/S) have captured numerous attention. But, they suffered from shuttle effect and surface passivation. RT-Na/S show inferior energy-storage abilities, ascribed to the larger radii of Na-ions. Herein, the vigorous review is displayed from different kinds of metal-based traits, containing single metal, metal-based samples, and multifunctional hybrids. Through the controlling of structures and composition, the conversion reaction about liquid/solid phases would be enhanced, accompanied by the enhancements of cycling stabilities and rate properties, which enables the break-through of practical applications. The in-depth influences of catalytic effects on the Na-S reaction mechanism and the corresponding electrochemical performance in recently representative works are systematically reviewed. Particularly, this review is anticipated to propose potential research directions for further enhancement of RT-Na/S batteries.