A High-Performance Primary Nanosheet Heterojunction Cathode Composed of Na0.44 MnO2 Tunnels and Layered Na2 Mn3 O7 for Na-Ion Batteries

New insights into tunnel-type NaxMnO2-yFy with high performance and excellent cycling stability: the impact of F-doping

Developing sustainable batteries based on abundant elements such as sodium and manganese is very attractive. Thus, sodium-manganese oxides can be employed as electrodes for sodium-ion batteries. Herein, an NaxMnO2-yFy electrode material is investigated and optimized. Galvanostatic cycling and diffusion coefficient calculations have been employed. It is found that tailoring the stoichiometry using the sodium/manganese ratio and fluorine content in the synthesis can improve the electrochemical performance and achieve high capacity and superb cycling stability. An anion-doping strategy (F-doping) can significantly improve electrode stability, and greatly raise the maximum specific capacity from ca. 70 mA h g-1 for an F-free sample to ca. 120 mA h g-1 for an F-doped sample at a slow rate (10 mA g-1 of current intensity). The reversible capacity of the F-doped sample is stable for many cycles (around 40-45 mA h g-1 at 500 mA g-1 for 1000 cycles).

High-performance heterostructure Na0.7MnO2.05-Na0.91MnO2 as a lithium-free cathode for lithium-ion batteries

In this investigation, a lithium-free cathode material, Na0.7MnO2.05-Na0.91MnO2, was synthesized by the solid phase method. The intercalation mechanism and partial phase transformation mechanism of NMO600 were clarified by in situ X-ray diffraction and impedance. The design of the heterostructure is favourable for improving the lithium ion storage of NMO600, which can deliver a discharge capacity of 83.12 mA h g-1 at 1 A g-1 and keep 61.71 mA h g-1 after 700 cycles.

Review and New Perspectives on Non-Layered Manganese Compounds as Electrode Material for Sodium-Ion Batteries

After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerging in the market. This is a result of the concerns regarding sustainability and production costs of the former, as well as issues related to safety and toxicity. Electrode materials for the new sodium-ion batteries may contain available and sustainable elements such as sodium itself, as well as iron or manganese, while eliminating the common cobalt cathode compounds and copper anode current collectors for lithium-ion batteries. The multiple oxidation states, abundance, and availability of manganese favor its use, as it was shown early on for primary batteries. Regarding structural considerations, an extraordinarily successful group of cathode materials are layered oxides of sodium, and transition metals, with manganese being the major component. However, other technologies point towards Prussian blue analogs, NASICON-related phosphates, and fluorophosphates. The role of manganese in these structural families and other oxide or halide compounds has until now not been fully explored. In this direction, the present review paper deals with the different Mn-containing solids with a non-layered structure already evaluated. The study aims to systematize the current knowledge on this topic and highlight new possibilities for further study, such as the concept of entatic state applied to electrodes.

Recent Advances in Sodium-Ion Batteries: Cathode Materials

Emerging energy storage systems have received significant attention along with the development of renewable energy, thereby creating a green energy platform for humans. Lithium-ion batteries (LIBs) are commonly used, such as in smartphones, tablets, earphones, and electric vehicles. However, lithium has certain limitations including safety, cost-effectiveness, and environmental issues. Sodium is believed to be an ideal replacement for lithium owing to its infinite abundance, safety, low cost, environmental friendliness, and energy storage behavior similar to that of lithium. Inhered in the achievement in the development of LIBs, sodium-ion batteries (SIBs) have rapidly evolved to be commercialized. Among the cathode, anode, and electrolyte, the cathode remains a significant challenge for achieving a stable, high-rate, and high-capacity device. In this review, recent advances in the development and optimization of cathode materials, including inorganic, organometallic, and organic materials, are discussed for SIBs. In addition, the challenges and strategies for enhancing the stability and performance of SIBs are highlighted.

Strategies to mitigate the shuttle effect in room temperature sodium-sulfur batteries: improving cathode materials

Room-temperature sodium-sulfur batteries (RT-Na/S batteries) with high reversible capacity (1675 mA h g^-1) and excellent energy density (1274 W h kg^-1) based on abundant resources of the metal Na have become a research hotspot recently. However, the intermediate product sodium polysulfides (NaPSs) generated during the charge-discharge process are easily dissolved in the ether electrolyte and transferred from the sulfur cathode to the metallic sodium surface, resulting in rapid capacity decay (shuttle effect), which seriously affects the practical application of RT-Na/S batteries. Herein, the mechanism and recent research progress in suppressing the shuttle effect of the sulfur cathode in RT-Na/S batteries are summarized. Strategies such as carbon-based materials physically fixing NaPSs, polar materials absorbing NaPSs to reduce their dissolution, and catalytic materials accelerating the transformation of NaPSs into final products are provided. Challenges and insights into high-performance sulfur electrodes for optimizing RT-Na/S batteries are discussed.

Sol-gel research in China: a brief history and recent research trends in synthesis of sol-gel derived materials and their applications

The sol-gel process has become a rapidly growing research area in materials science. A variety of materials prepared via sol-gel routes have shown unique properties and characteristics that are difficult to achieve using conventional methods. In recent years, tremendous progress in sol-gel R&D has been made not only in the world but also in China. Here, this review provides a retrospective overview of the sol-gel history in China and summarizes recent progress and applications of sol-gel research in Chinese universities, institutes, and industries. It highlights some of the recent developments published by Chinese researchers in the last 5 years, ranging from the sol-gel synthesis of nanomaterials, bulk materials, and functional coatings, to their applications in the fields of energy conversion, energy storage, photocatalysis, etc. It is evident that sol-gel technology nowadays in China has evolved into a vibrant research area both in academia and industry. Graphical abstract.

Design and synthesis of high-energy-density heterostructure Na0.7MnO2–Li4Mn5O12 cathode material for advanced lithium batteries

The construction of the heterostructure, 0.6Na0.7MnO2–0.4Li4Mn5O12, can form a synergistic effect, which exhibits superior high-rate capability and excellent cycle performance.

Advanced cobalt-free cathode materials for sodium-ion batteries

Attempts to utilize lithium-ion batteries (LIBs) in large-scale electrochemical energy storage systems have achieved initial success, and solid-state LIBs using metallic lithium as the anode have also been well developed. However, the sharply increased demands/costs and the limited reserves of the two most important metal elements (Li & Co) for LIBs have raised concerns about future development. Sodium-ion batteries (SIBs) equipped with advanced cobalt-free cathodes show great potential in solving both "lithium panic" and "cobalt panic", and have made remarkable progress in recent years. In this review, we comprehensively summarize the recent advances of high-performance cobalt-free cathode materials for advanced SIBs, systematically analyze the conflicts of structural/electrochemical stability with intrinsic insufficiencies of cobalt-free cathode materials, and extensively discuss the strategies of constructing stable cobalt-free cathode materials by making full use of non-cobalt transition-metal elements and suitable crystal structures, all of which aim to provide insights into the key factors (e.g., phase transformation, particle cracks, crystal defects, lattice distortion, lattice oxygen oxidation, morphology, transition-metal migration/dissolution, and the synergistic effects of composite structures) that can determine the stability of cobalt-free cathode materials, provide guidelines for future research, and stimulate more interest on constructing high-performance cobalt-free cathode materials.

Chemical Heterointerface Engineering on Hybrid Electrode Materials for Electrochemical Energy Storage

The chemical heterointerfaces in hybrid electrode materials play an important role in overcoming the intrinsic drawbacks of individual materials and thus expedite the in-depth development of electrochemical energy storage. Benefiting from the three enhancement effects of accelerating charge transport, increasing the number of storage sites, and reinforcing structural stability, the chemical heterointerfaces have attracted extensive interest and the electrochemical performances of hybrid electrode materials have been significantly optimized. In this review, recent advances regarding chemical heterointerface engineering in hybrid electrode materials are systematically summarized. Especially, the intrinsic behaviors of chemical heterointerfaces on hybrid electrode materials are refined based on built-in electric field, van der Waals interaction, lattice mismatch and connection, electron cloud bias and chemical bond, and their combination. The strategies for introducing chemical heterointerfaces are classified into in situ local transformation, in situ growth, cosynthesis, and other strategy. The recent progress about the chemical heterointerfaces engineering specially focusing on metal-ion batteries, supercapacitors, and Li-S batteries are introduced in detail. Furthermore, the classification and characterization of chemical heterointerfaces are briefly described. Finally, the emerging challenges and perspectives about future directions of chemical heterointerface engineering are proposed.