2020 roadmap on two-dimensional materials for energy storage and conversion

Energy storage and conversion have attained significant interest owing to its important applications that reduce CO₂ emission through employing green energy. Some promising technologies are included metal-air batteries, metal-sulfur batteries, metal-ion batteries, electrochemical capacitors, etc. Here, metal elements are involved with lithium, sodium, and magnesium. For these devices, electrode materials are of importance to obtain high performance. Two-dimensional (2D) materials are a large kind of layered structured materials with promising future as energy storage materials, which include graphene, black phosporus, MXenes, covalent organic frameworks (COFs), 2D oxides, 2D chalcogenides, and others. Great progress has been achieved to go ahead for 2D materials in energy storage and conversion. More researchers will join in this research field. Under the background, it has motivated us to contribute with a roadmap on ‘two-dimensional materials for energy storage and conversion.     

Progress of Organic Electrodes in Aqueous Electrolyte for Energy Storage and Conversion

Aqueous batteries using inorganic compounds as electrode materials are considered a promising solution for grid-scale energy storage, while wide application is limited by the short life and/or high cost of electrodes. Organics with carbonyl groups are being investigated as the alternative to inorganic electrode materials because they offer the advantages of tunable structures, renewability, and they are environmentally benign. Furthermore, the wide internal space of such organic materials enables flexible storage of various charged ions (for example, H⁺, Li⁺, Na⁺, K⁺, Zn²⁺, Mg²⁺, and Ca²⁺, and so on). We offer a comprehensive overview of the progress of organics containing carbonyls for energy storage and conversion in aqueous electrolytes, including applications in aqueous batteries as solid-state electrodes, in flow batteries as soluble redox species, and in water electrolysis as redox buffer electrodes. The advantages of organic electrodes are summarized, with a discussion of the challenges remaining for their practical application.     

2D Materials as Ionic Sieves for Inhibiting the Shuttle Effect in Batteries

Alternatives of commercial lithium‐ion batteries (LIBs) have drawn huge attention due to the large demand of energy storage systems and the lack of resources for traditional LIBs. Promising candidates include but are not limited to Li‐S batteries, organic batteries and flow batteries. However, the dissolution of active materials and the consequent shuttle effect, as one of the main challenges in these candidates, always leads to significant capacity loss and poor cycling life. The rising two‐dimensional (2D) materials, with well‐defined structures and attractive physical and chemical properties, provide a new vision to solve these problems via suppressing the shuttle of the dissolved active materials. Herein, we present a minireview on the advances and perspectives of 2D materials as ionic sieves for inhibiting the shuttle effect in batteries.     

Sulfur‐Based Electrodes that Function via Multielectron Reactions for Room‐Temperature Sodium‐Ion Storage

Emerging rechargeable sodium‐ion storage systems—sodium‐ion and room‐temperature sodium–sulfur (RT‐NaS) batteries—are gaining extensive research interest as low‐cost options for large‐scale energy‐storage applications. Owing to their abundance, easy accessibility, and unique physical and chemical properties, sulfur‐based materials, in particular metal sulfides (MS_x) and elemental sulfur (S), are currently regarded as promising electrode candidates for Na‐storage technologies with high capacity and excellent redox reversibility based on multielectron conversion reactions. Here, we present current understanding of Na‐storage mechanisms of the S‐based electrode materials. Recent progress and strategies for improving electronic conductivity and tolerating volume variations of the MS_x anodes in Na‐ion batteries are reviewed. In addition, current advances on S cathodes in RT‐NaS batteries are presented. We outline a novel emerging concept of integrating MS_x electrocatalysts into conventional carbonaceous matrices as effective polarized S hosts in RT‐NaS batteries as well. This comprehensive progress report could provide guidance for research toward the development of S‐based materials for the future Na‐storage techniques.     

A review of transition metal chalcogenide/graphene nanocomposites for energy storage and conversion

Recent advances in the applications of transition metal chalcogenides/graphene (TMC/graphene) nanocomposites in future energy storage and conversion are reviewed. The synthesis processes and structures of TMC/graphene, workingpriciple of evergy energy device, and the electrochemical performances are summarized.     

MXene-Based Nanocomposites for Energy Conversion and Storage Applications

Novel nanomaterials and advanced nanotechnology continuously push forward the rapid development of sustainable energy conversion and storage equipment. An emerging family of two-dimensional transition-metal carbides, nitrides and carbonitrides, also known as MXenes, have attracted increasing attention and in depth investigation. Benefitting from their unique intrinsic properties, MXenes have attracted significant attention and they have been considered as promising candidate materials for the development of environmentally friendly energy resources. A large number of studies show that MXenes have great potential in energy conversion and storage fields. Despite of their exceptional properties, MXenes also have some inherent characteristics, such as low capacities and unstable retention performances, which severely hinder their prospect applications in energy conversion and storage fields. In this Minireview, the latest progress on MXenes and their hybrid composites with small molecules, polymers, carbon or metal ions, and their applications in energy conversion and storage fields is highlighted, including their use in different types of batteries, supercapacitors, hydrogen/oxygen evolution reactions, electromagnetic interference absorption/shielding and solar steam generation. In addition, the critical challenges and further development prospects of MXene-based materials are also introduced.     

High‐Capacity Anode Materials for Sodium‐Ion Batteries

Na‐ion batteries are an attractive alternative to Li‐ion batteries for large‐scale energy storage systems because of their low cost and the abundant Na resources. This Review provides a comprehensive overview of selected anode materials with high reversible capacities that can increase the energy density of Na‐ion batteries. Moreover, we discuss the reaction and failure mechanisms of those anode materials with a view to suggesting promising strategies for improving their electrochemical performance.     

Lithium–Sulfur Batteries under Lean Electrolyte Conditions: Challenges and Opportunities

The development of energy‐storage devices has received increasing attention as a transformative technology to realize a low‐carbon economy and sustainable energy supply. Lithium–sulfur (Li–S) batteries are considered to be one of the most promising next‐generation energy‐storage devices due to their ultrahigh energy density. Despite the extraordinary progress in the last few years, the actual energy density of Li–S batteries is still far from satisfactory to meet the demand for practical applications. Considering the sulfur electrochemistry is highly dependent on solid‐liquid‐solid multi‐phase conversion, the electrolyte amount plays a primary role in the practical performances of Li–S cells. Therefore, a lean electrolyte volume with low electrolyte/sulfur ratio is essential for practical Li–S batteries, yet under these conditions it is highly challenging to achieve acceptable electrochemical performances regarding sulfur kinetics, discharge capacity, Coulombic efficiency, and cycling stability especially for high‐sulfur‐loading cathodes. In this Review, the impact of the electrolyte/sulfur ratio on the actual energy density and the economic cost of Li–S batteries is addressed. Challenges and recent progress are presented in terms of the sulfur electrochemical processes: the dissolution–precipitation conversion and the solid–solid multi‐phasic transition. Finally, prospects of future lean‐electrolyte Li–S battery design and engineering are discussed.     

Graphene-based electrochemical energy conversion and storage: fuel cells, supercapacitors and lithium ion batteries

Graphene has attracted extensive research interest due to its strictly 2-dimensional (2D) structure, which results in its unique electronic, thermal, mechanical, and chemical properties and potential technical applications. These remarkable characteristics of graphene, along with the inherent benefits of a carbon material, make it a promising candidate for application in electrochemical energy devices. This article reviews the methods of graphene preparation, introduces the unique electrochemical behavior of graphene, and summarizes the recent research and development on graphene-based fuel cells, supercapacitors and lithium ion batteries. In addition, promising areas are identified for the future development of graphene-based materials in electrochemical energy conversion and storage systems.     

Silica-Derived Nanostructured Electrode Materials for ORR,OER, HER,CO2RR Electrocatalysis,and Energy Storage Applications: A Review**

Silica-derived nanostructured catalysts (SDNCs) are a class of materials synthesized using nanocasting and templating techniques, which involve the sacrificial removal of a silica template to generate highly porous nanostructured materials. The surface of these nanostructures is functionalized with a variety of electrocatalytically active metal and non-metal atoms. SDNCs have attracted considerable attention due to their unique physicochemical properties, tunable electronic configuration, and microstructure. These properties make them highly efficient catalysts and promising electrode materials for next generation electrocatalysis, energy conversion, and energy storage technologies. The continued development of SDNCs is likely to lead to new and improved electrocatalysts and electrode materials. This review article provides a comprehensive overview of the recent advances in the development of SDNCs for electrocatalysis and energy storage applications. It analyzes 337,061 research articles published in the Web of Science (WoS) database up to December 2022 using the keywords “silica”, “electrocatalysts”, “ORR”, “OER”, “HER”, “HOR”, “CO₂RR”, “batteries”, and “supercapacitors”. The review discusses the application of SDNCs for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂RR), supercapacitors, lithium-ion batteries, and thermal energy storage applications. It concludes by discussing the advantages and limitations of SDNCs for energy applications.     

MXenes及MXenes复合材料的制备及其在能量存储与转换中的应用

综述了新型过渡金属碳化物和/或氮化物(MXenes)二维纳米材料的合成及其在电化学能源存储与转换中应用的研究进展,这些应用可以分为如下三类:二次电池、超级电容器以及电化学催化。 由于具有二维结构、金属导电性、亲水性表面以及其它优点,MXene二维纳米材料在这些应用领域展示了良好的性能,而且还可以通过嵌入、复合、掺杂、组装等方法来进一步提高其电化学性能。 本文为新型MXenes以及相关材料的开发、合成和应用提供了思路,这种新型MXenes 材料可以用于能量存储与转换、电子和催化等领域。     

Mixed Transition‐Metal Oxides: Design,Synthesis, and Energy‐Related Applications

A promising family of mixed transition‐metal oxides (MTMOs) (designated as A_xB_3‐xO₄; A, B=Co, Ni, Zn, Mn, Fe, etc.) with stoichiometric or even non‐stoichiometric compositions, typically in a spinel structure, has recently attracted increasing research interest worldwide. Benefiting from their remarkable electrochemical properties, these MTMOs will play significant roles for low‐cost and environmentally friendly energy storage/conversion technologies. In this Review, we summarize recent research advances in the rational design and efficient synthesis of MTMOs with controlled shapes, sizes, compositions, and micro‐/nanostructures, along with their applications as electrode materials for lithium‐ion batteries and electrochemical capacitors, and efficient electrocatalysts for the oxygen reduction reaction in metal–air batteries and fuel cells. Some future trends and prospects to further develop advanced MTMOs for next‐generation electrochemical energy storage/conversion systems are also presented.     

Progress and Prospects on the Fabrication of Graphene-Based Nanostructures for Energy Storage,Energy Conversion and Biomedical Applications

Graphene, a two-dimensional (2D) layered material has attracted much attention from the scientific community due to its exceptional electrical, thermal, mechanical, biological and optical properties. Hence, numerous applications utilizing graphene-based materials could be conceived in next-generation electronics, chemical and biological sensing, energy conversion and storage, and beyond. The interaction between graphene surfaces with other materials plays a vital role in influencing its properties than other bulk materials. In this review, we outline the recent progress in the production of graphene and related 2D materials, and their uses in energy conversion (solar cells, fuel cells), energy storage (batteries, supercapacitors) and biomedical applications.     

Design Concepts of Transition Metal Dichalcogenides for High-Performance Aqueous Zn-Ion Storage

Aqueous Zn-ion batteries (AZIBs) are considered as promising large-scale energy storage devices due to their high safety and low cost. Transition metal dichalcogenides (TMDs) as the potential aqueous Zn-storage cathode materials are under the research spotlight because of their facile 2D ion-transport channels and weak electrostatic interactions with Zn²⁺. In this concept article, we summarize the intrinsic structural features and aqueous Zn-storage mechanisms of the TMDs-based electrodes. More significantly, the latest design concepts of TMDs materials for high-performance AZIBs are discussed in detail from three aspects of interlayer expansion engineering, phase transition engineering, and structure defects engineering. Finally, the current challenges facing TMDs cathodes and possible remedies are outlined for future developments towards efficient, rapid, and stable aqueous Zn-ion storage.     

A High-Energy Aqueous All-Sulfur Battery

Rechargeable aqueous batteries are promising energy storage devices because of their high safety and low cost. However, their energy densities are generally unsatisfactory due to the limited capacities of ion-inserted electrode materials, prohibiting their widespread applications. Herein, a high-energy aqueous all-sulfur battery was constructed via matching S/Cu₂S and S/CaS_x redox couples. In such batteries, both cathodes and anodes undergo the conversion reaction between sulfur/metal sulfides redox couples, which display high specific capacities and rational electrode potential difference. Furthermore, during the charge/discharge process, the simultaneous redox of Cu²⁺ ion charge-carriers also takes place and contributes to a more two-electron transfer, which doubles the capacity of cathodes. As a result, the assembled aqueous all-sulfur batteries deliver a high discharge capacity of 447 mAh g⁻¹ based on total mass of sulfur in cathode and anode at 0.1 A g⁻¹, contributing to an enhanced energy density of 393 Wh kg⁻¹. This work will widen the scope for the design of high-energy aqueous batteries.     

Energy Storage Materials Synthesized from Ionic Liquids

The advent of ionic liquids (ILs) as eco‐friendly and promising reaction media has opened new frontiers in the field of electrochemical energy storage. Beyond their use as electrolyte components in batteries and supercapacitors, ILs have unique properties that make them suitable as functional advanced materials, media for materials production, and components for preparing highly engineered functional products. Aiming at offering an in‐depth review on the newly emerging IL‐based green synthesis processes of energy storage materials, this Review provides an overview of the role of ILs in the synthesis of materials for batteries, supercapacitors, and green electrode processing. It is expected that this Review will assess the status quo of the research field and thereby stimulate new thoughts and ideas on the emerging challenges and opportunities of IL‐based syntheses of energy materials.     

2D MXenes Nanosheets for Advanced Energy Conversion and Storage Devices: Recent Advances and Future Prospects

Since the initial MXenes were discovered in 2011, several MXene compositions constructed using combinations of various transition metals have been developed. MXenes are ideal candidates for different applications in energy conversion and storage, because of their unique and interesting characteristics, which included good electrical conductivity, hydrophilicity, and simplicity of large-scale synthesis. Herein, we study the current developments in two-dimensional (2D) MXene nanosheets for energy storage and conversion technologies. First, we discuss the introduction to energy storage and conversion devices. Later, we emphasized on 2D MXenes and some specific properties of MXenes. Subsequently, research advances in MXene-based electrode materials for energy storage such as supercapacitors and rechargeable batteries is summarized. We provide the relevant energy storage processes, common challenges, and potential approaches to an acceptable solution for 2D MXene-based energy storage. In addition, recent advances for MXenes used in energy conversion devices like solar cells, fuel cells and catalysis is also summarized. Finally, the future prospective of growing MXene-based energy conversion and storage are highlighted.     

钠离子电池用铁基正极材料的研究进展

气候变化和化石燃料枯竭等问题将促进新型绿色能源的开发和利用。因此,高效率、低成本、安全的储能系统,得到了越来越多的关注和研究。在各类储能系统中,二次电池是存储电能、为电子设备供电的最理想选择。目前,锂离子电池(LIBs)的应用最广泛。然而,地球上锂资源的短缺和分布不均造成的成本较高,急需研究和开发其他高性能的新型二次电池。钠元素具有地壳中储量丰富、均匀且与锂具有相似化学性质等优势,使得钠离子电池(SIBs)成为了取代LIBs最有前景的备选二次电池之一。然而,钠离子的体积较大、离子传导动力学更缓慢、导电性更差等问题,限制了SIBs高性能的实现,这是目前研究的难点和重点。此外,铁具有储量丰富、环境友好的特点,其在SIBs中的应用引起了电池领域科研工作者的广泛关注。因此,寻找良好的铁基正极材料成为SIBs高性能电极材料开发的一个重要研究方向。本综述对近年来SIBs铁基正极材料方面的研究进展进行了总结,并按照聚阴离子型化合物、过渡金属氧化物、普鲁士蓝及类似物和氟化物分类,进行了系统的阐述和分析。     

Advances in the Cathode Materials for Lithium Rechargeable Batteries

The accelerating development of technologies requires a significant energy consumption, and consequently the demand for advanced energy storage devices is increasing at a high rate. In the last two decades, lithium‐ion batteries have been the most robust technology, supplying high energy and power density. Improving cathode materials is one of the ways to satisfy the need for even better batteries. Therefore developing new types of positive electrode materials by increasing cell voltage and capacity with stability is the best way towards the next‐generation Li rechargeable batteries. To achieve this goal, understanding the principles of the materials and recognizing the problems confronting the state‐of‐the‐art cathode materials are essential prerequisites. This Review presents various high‐energy cathode materials which can be used to build next‐generation lithium‐ion batteries. It includes nickel and lithium‐rich layered oxide materials, high voltage spinel oxides, polyanion, cation disordered rock‐salt oxides and conversion materials. Particular emphasis is given to the general reaction and degradation mechanisms during the operation as well as the main challenges and strategies to overcome the drawbacks of these materials.     

An Ultrastable Anode for Long‐Life Room‐Temperature Sodium‐Ion Batteries

Sodium‐ion batteries are important alternative energy storage devices that have recently come again into focus for the development of large‐scale energy storage devices because sodium is an abundant and low‐cost material. However, the development of electrode materials with long‐term stability has remained a great challenge. A novel negative‐electrode material, a P2‐type layered oxide with the chemical composition Na_2/3Co_1/3Ti_2/3O₂, exhibits outstanding cycle stability (ca. 84.84 % capacity retention for 3000 cycles, very small decrease in the volume (0.046 %) after 500 cycles), good rate capability (ca. 41 % capacity retention at a discharge/charge rate of 10 C), and a usable reversible capacity of about 90 mAh g^?1 with a safe average storage voltage of approximately 0.7 V in the sodium half‐cell. This P2‐type layered oxide is a promising anode material for sodium‐ion batteries with a long cycle life and should greatly promote the development of room‐temperature sodium‐ion batteries.