Hydroborate/carborate electrolytes represent an emerging and newly rediscovered solid electrolyte used in various all-solid-state batteries (such as lithium-ion batteries and sodium-ion batteries). High ionic conductivity, wide chemical/electrochemical stability, low density, and favorable mechanical properties make hydroborate/carborate electrolytes a promising candidate for solving the difficult challenges faced by the device integration and processing of all-solid-state batteries. It is remarkable that the ionic conductivity of solid electrolytes can be simply adjusted up to 10−3 S cm−1, and the optimized ionic conductivity can even reach 10−2 S cm−1. Furthermore, hydroborate/carborate electrolytes have been successfully formed and applied to ~ 5 V high-voltage solid-state batteries. However, due to certain characteristics of hydroborate/carborate electrolytes, such as anion rotation and phase transition, it is challenging to understand the mechanism of their high ionic conductivity. Therefore, in this review, we summarized the latest research progress on hydroborate/carborate electrolytes, highlighted various mechanisms underlying the conductivity, described emerging characterization techniques and theoretical calculations, and listed general guidelines to unravel the high conductivity of hydroborate/carborate compounds. Novel strategies and suggestions on hydroborate/carborate work are also proposed. Following emerging research trends, we project promising future development toward the realization of hydroborate/carborate electrolytes in practical applications.
Proton exchange membrane fuel cells (PEMFCs) are becoming a major part of a greener and more sustainable future. However, the costs of high-purity hydrogen and noble metal catalysts alongside the complexity of the PEMFC system severely hamper their commercialization. Operating PEMFCs at high temperatures (HT-PEMFCs, above 120 °C) brings several advantages, such as increased tolerance to contaminants, more affordable catalysts, and operations without liquid water, hence considerably simplifying the system. While recent progresses in proton exchange membranes for HT-PEMFCs have made this technology more viable, the HT-PEMFC viscous acid electrolyte lowers the active site utilization by unevenly diffusing into the catalyst layer while it acutely poisons the catalytic sites. In recent years, the synthesis of platinum group metal (PGM) and PGM-free catalysts with higher acid tolerance and phosphate-promoted oxygen reduction reaction, in conjunction with the design of catalyst layers with improved acid distribution and more triple-phase boundaries, has provided great opportunities for more efficient HT-PEMFCs. The progress in these two interconnected fields is reviewed here, with recommendations for the most promising routes worthy of further investigation. Using these approaches, the performance and durability of HT-PEMFCs will be significantly improved.
Rechargeable room-temperature sodium–sulfur (Na–S) and sodium–selenium (Na–Se) batteries are gaining extensive attention for potential large-scale energy storage applications owing to their low cost and high theoretical energy density. Optimization of electrode materials and investigation of mechanisms are essential to achieve high energy density and long-term cycling stability of Na–S(Se) batteries. Herein, we provide a comprehensive review of the recent progress in Na–S(Se) batteries. We elucidate the Na storage mechanisms and improvement strategies for battery performance. In particular, we discuss the advances in the development of battery components, including high-performance sulfur cathodes, optimized electrolytes, advanced Na metal anodes and modified separators. Combined with current research achievements, this review outlines remaining challenges and clear research directions for the future development of practical high-performance Na–S(Se) batteries.
To realize a low-carbon economy and sustainable energy supply, the development of energy storage devices has aroused intensive attention. Lithium-sulfur (Li-S) batteries are regarded as one of the most promising next-generation battery devices because of their remarkable theoretical energy density, cost-effectiveness, and environmental benignity. However, the practical application of Li-S batteries is hindered by such challenges as low sulfur utilization (< 80%), fast capacity fade, short service life (< 200 redox cycles), and severe self-discharge. The reasons behind the challenges are: (1) low conductivity of the active materials, (2) large volume changes during redox cycling, (3) serious polysulfide shuttling and, (4) lithium-metal anode contamination/corrosion and dendrite formation. Significant achievements have been made to address these problems in the past decade. In this review, the recent advances in material synthesis and technology development are analysed in terms of the electrochemical performance of different Li-S battery components. The critical analysis was conducted based on the merits and shortcomings of the reported work on the issues facing the individual component. A versatile 3D-printing technique is also examined on its practicability for Li-S battery production. The insights on the rational structural design and reasonable parameters for Li-S batteries are highlighted along with the “five 5s” concept from a practical point of view. The remaining challenges are outlined for researchers to devote more efforts on the understanding and commercialization of the devices in terms of the material preparation, cell manufacturing, and characterization.
The low-temperature electrolysis of CO2 in membrane-based flow reactors is a promising technology for converting captured CO2 into valuable chemicals and fuels. In recent years, substantial improvements in reactor design have significantly improved the economic viability of this technology; thus, the field has experienced a rapid increase in research interest. Among the factors related to reactor design, the ion exchange membrane (IEM) plays a prominent role in the energetic efficiency of CO2 conversion into useful products. Reactors utilizing cation exchange, anion exchange and bipolar membranes have all been developed, each providing unique benefits and challenges that must be overcome before large-scale commercialization is feasible. Therefore, to direct advances in IEM technology specific to electrochemical CO2 reduction reactions (CO2RRs), this review serves to first provide polymer scientists with a general understanding of membrane-based CO2RR reactors and membrane-related shortcomings and to encourage systematic synthetic approaches to develop membranes that meet the specific requirements of CO2RRs. Second, this review provides researchers in the fields of electrocatalysis and CO2RRs with more detailed insight into the often-overlooked membrane roles and requirements; thus, new methodologies for membrane evaluation during CO2RR may be developed. By using CO2-to-CO/HCOO− methodologies as practical baseline systems, a clear conceptualization of the merits and challenges of different systems and reasonable objectives for future research and development are presented.
In the last 20 years, direct alcohol fuel cells (DAFCs) have been the subject of tremendous research efforts for the potential application as on-demand power sources. Two leading technologies respectively based on proton exchange membranes (PEMs) and anion exchange membranes (AEMs) have emerged: the first one operating in an acidic environment and conducting protons; the second one operating in alkaline electrolytes and conducting hydroxyl ions. In this review, we present an analysis of the state-of-the-art acidic and alkaline DAFCs fed with methanol and ethanol with the purpose to support a comparative analysis of acidic and alkaline systems, which is missing in the current literature. A special focus is placed on the effect of the reaction stoichiometry in acidic and alkaline systems. Particularly, we point out that, in alkaline systems, OH− participates stoichiometrically to reactions, and that alcohol oxidation products are anions. This aspect must be considered when designing the fuel and when making an energy evaluation from a whole system perspective.
Ammonia is considered as an alternative fuel resource for a sustainable green future. The production of ammonia involves the electrochemical nitrogen reduction reaction (NRR), which has gained considerable attention due to its eco-friendly resources and nonharmful byproducts. Even with the manifold works on NRR, the technique has not reached the industrial scale because of the impediments of NRR electrocatalysts, and in addition, state-of-the-art electrocatalysts have not yet been discovered. In this review, first, the mechanism of the NRR, key metrics, and operational procedures for NRR electrochemistry are presented. Then, the electrocatalyst designs for efficient NRR are briefly introduced, followed by a discussion on the influence of the electrolytes that enhance NRR performance. The counterion effects of electrolytes on NRR performance and strategies for suppressing the HER by electrolyte additives are also discussed. Later, the NRR mechanisms are upgraded, and a comprehensive review of metal-N2 batteries is provided. This review summarizes the effective methods for performing the NRR and strategies to suppress the HER on various electrocatalysts by tuning electrolytes and their additives. The review concludes by discussing the prospects of metal-N2 batteries.
Zn-air batteries are highly attractive for direct chemical-to-electrical energy conversion and for solving the energy crisis and environmental problems. Designing efficient oxygen electrodes has been considered one of the most critical steps in the development of advanced Zn-air batteries because of the sluggish kinetics of the oxygen reduction reaction and the oxygen evolution reaction. In recent years, nanostructured carbon-based electrodes with large surface areas, efficient oxygen-catalytic centers, and hierarchically porous matrices have provided significant opportunities to optimize the performance of the oxygen electrodes in both primary and rechargeable Zn-air batteries. In this review, we provide a comprehensive summary of the reported nanostructured carbon-based electrodes for advanced Zn-air batteries in terms of tailoring the oxygen-catalytic sites and designing carbon supports. The versatile synthetic strategies, characterization methods, and in-depth understanding of the relationships between the oxygen-catalytic sites/nanostructures and the oxygen electrode performance are systematically summarized. Furthermore, we also briefly outline recent progress in engineering flexible and high-power Zn-air batteries. Ultimately, a thorough discussion of current primary challenges and future perspectives on the rational design of nanostructured carbon-based oxygen electrodes is given, thus providing inspiration for the future prosperity of fast-kinetic and efficient Zn-air batteries in a broad range of energy fields.
Li metal anodes have attracted tremendous attention in the last decade because of their high theoretical capacities and low electrochemical potentials. However, until now, there has only been limited success in improving the interfacial and structural stabilities and in realizing the highly controllable and large-scale fabrication of this emerging material; these limitations have posed great obstacles to further performing fundamental and applied studies in Li metal anodes. In this review, we focus on summarizing the existing challenges of Li metal anodes based on the leap from coin cells to pouch cells and on outlining typical methods for designing Li metal anodes on demand; we controllably engineer their surface protection layers and structure sizes by encapsulating structured Li metal inside a variety of synthetic protection layers. We aim to provide a comprehensive understanding and serve as a strategic guide for designing and fabricating practicable Li metal anodes for use in pouch batteries. Challenges and opportunities regarding this burgeoning field are critically evaluated at the end of this review.
Li metal anode has attracted tremendous attention in the last decade because of its high theoretical capacity and low electrochemical potential. However, till now, there is only limited success in improving its interface stability and structure stability, as well as realizing the highly controllable and large-scaled fabrication of this emerging material, posing great obstacles to further promoting its fundamental and applied studies. In this review, we focus on summarizing the existing challenges of Li metal anode based on the leap from coin cells to pouch cells and outlining the typical solutions for designing Li metal anode on-demand through controllably engineering its surface protection layer and structure size, which trend is encapsulating structured Li metal inside a variety of synthetic protection layer. We aim to provide a comprehensive understanding and serve as a strategic guidance for designing and fabricating practicable Li metal anode using in pouch batteries. Challenges and opportunities regarding this burgeoning field are also critically evaluated at the end of this review.
The advantages of zero emission and high energy efficiency make proton exchange membrane fuel cells (PEMFCs) promising options for future energy conversion devices. To address the cost issue associated with Pt-based electrocatalysts, considerable effort over the past several years has been devoted to catalyst surface modification by means of novel electrocatalysts, such as solid catalysts with an ionic liquid layer (SCILL), which improves both the oxygen reduction reaction (ORR) activity and durability. However, despite numerous reports of dramatically enhanced ORR activity, as determined via the rotating disk electrode (RDE) method, few studies on the application of SCILLs in membrane electrode assembly (MEA) have been reported. The underlying reason lies in the well-acknowledged technological gap between half-cells and full-cells, which originates from the disparate microenvironments for three phase boundaries. Therefore, the objective of this review is to compare the detailed information about improvements in fuel cell performance in both half- and full-cells, thus increasing the fundamental understanding of the mechanism of SCILL. In this review, the concept of SCILL and its origin are introduced, the outstanding electrochemical performance of SCILL catalysts in both RDE and MEA measurements is summarized, and the durability of SCILL catalysts is analysed. Subsequently, proposed mechanisms for the enhanced ORR activity in half-cells, the improved oxygen transport in full-cells and the boosted stability of SCILL catalysts are discussed, while the effects of the IL chemical structure, IL loading as well as the operating conditions on the performance and lifetime of SCILL catalysts are assessed. Finally, comprehensive conclusions are presented, and perspectives are proposed in the last section. It is believed that the new insight presented in this review could provide guidance for the further development of SCILLs in low-Pt PEMFCs.
Rechargeable aqueous zinc-ion batteries (ZIBs) have resurged in large-scale energy storage applications due to their intrinsic safety, affordability, competitive electrochemical performance, and environmental friendliness. Extensive efforts have been devoted to exploring high-performance cathodes and stable anodes. However, many fundamental issues still hinder the development of aqueous ZIBs. Here, we critically review and assess the energy storage chemistries of aqueous ZIBs for both cathodes and anodes. First, this review presents a comprehensive understanding of the cathode charge storage chemistry, probes the existing deficiencies in mechanism verification, and analyzes contradictions between the experimental results and proposed mechanisms. Then, a detailed summary of the representative cathode materials and corresponding comparative discussion is provided with typical cases encompassing structural features, electrochemical properties, existing drawbacks, and feasible remedies. Subsequently, the fundamental chemical properties, remaining challenges, and improvement strategies of both Zn metal and non-Zn anodes are presented to thoroughly explore the energy storage chemistry of ZIBs and pursue the development of high-performance ZIBs. Furthermore, the progress of mechanistic characterization techniques and theoretical simulation methods used for ZIBs is timely reviewed. Finally, we provide our perspectives, critical analysis, and insights on the remaining challenges and future directions for development of aqueous ZIBs.
As an indispensable part of the lithium-ion battery (LIB), a binder takes a small share of less than 3% (by weight) in the cell; however, it plays multiple roles. The binder is decisive in the slurry rheology, thus influencing the coating process and the resultant porous structures of electrodes. Usually, binders are considered to be inert in conventional LIBs. In the pursuit of higher energy density, many new binders are being developed for specific targets, such as the high-voltage (typically, $\geqslant$ 4.5 V) cathodes, conversion/alloy-type cathodes/anodes with large volume effect, and solid-state batteries (SSBs), in which these binders demonstrate their various functions. They may influence the solid electrolyte interface component, ensure the electrode/electrolyte interfacial stability, transport ions/electrons in the electrodes, provide adhesion and flexibility to solid-state electrolyte (SSE) films, etc. Here in this review, we try to summarize the advances on binders, among which the ones for high-voltage cathode materials, thick electrodes, micro-sized silicon particles, SSEs and SSBs are highlighted. We believe that the advanced functional binders would play decisive roles in the future development of high-energy–density LIBs and SSBs.
Binder usually takes a small part in batteries, while recent studies prove that it has multi-functions more than just adhesive.
With the increasing demand for low-cost and environmentally friendly energy, the application of rechargeable lithium-ion batteries (LIBs) as reliable energy storage devices in electric cars, portable electronic devices and space satellites is on the rise. Therefore, extensive and continuous research on new materials and fabrication methods is required to achieve the desired enhancement in their electrochemical performance. Battery active components, including the cathode, anode, electrolyte, and separator, play an important role in LIB functionality. The major problem of LIBs is the degradation of the electrolyte and electrode materials and their components during the charge‒discharge process. Atomic layer deposition (ALD) is considered a promising coating technology to deposit uniform, ultrathin films at the atomic level with controllable thickness and composition. Various metal films can be deposited on the surface of active electrodes and solid electrolyte materials to tailor and generate a protective layer at the electrode interface. In addition, synthesis of microbatteries and novel nanocomplexes of the cathode, anode, and solid-state electrolyte to enhance the battery performance can all be attained by ALD. Therefore, the ALD technique has great potential to revolutionize the future of the battery industry. This review article provides a comprehensive foundation of the current state of ALD in synthesizing and developing LIB active components. Additionally, new trends and future expectations for the further development of next-generation LIBs via ALD are reported.
In recent years, proton exchange membrane (PEM) fuel cells have regained worldwide attention from academia, industries, investors, and governments. The prospect of PEM fuel cells has turned into reality, with fuel cell vehicles successfully launched in the market. However, today’s fuel cells remain less competitive than combustion engines and batteries, primarily due to their high cost and short lifetime, which are significantly affected by the membrane electrode assembly (MEA), or the “chips” of PEM fuel cells. Therefore, many efforts have been devoted to developing advanced materials and manufacturing processes for MEAs. In this paper, we critically review the recent progress of key materials for MEAs, focusing on how to integrate materials into electrodes and MEAs. We also present the most advanced designs and manufacturing techniques of MEAs and discuss their possible constraints. Finally, perspectives on future R&D directions of materials and MEAs are provided. This review aims to bridge the gaps between academic material research and industrial manufacturing process development.
Among various rechargeable batteries, the lithium-ion battery (LIB) stands out due to its high energy density, long cycling life, in addition to other outstanding properties. However, the capacity of LIB drops dramatically at low temperatures (LTs) below 0 °C, thus restricting its applications as a reliable power source for electric vehicles in cold climates and equipment used in the aerospace. The electrolyte engineering has proved to be one of the most effective approaches to mitigate LIB performance degradation at LTs. In this review, we summarize the important factors contributing to the deterioration in Li+ transport and capacity utilization at LTs while systematically categorize the solvents, salts and additives reported in the literature. Strategies to improve the Li+ transport kinetics, in the bulk electrolyte and across the interphases, are discussed. In particular, the formation mechanism of solid electrolyte interphase and its functionality for LT electrolytes are analyzed. Perspectives on the future evolution of this area are also provided.
Solid-state batteries (SSBs) possess the advantages of high safety, high energy density and long cycle life, which hold great promise for future energy storage systems. The advent of printed electronics has transformed the paradigm of battery manufacturing as it offers a range of accessible, versatile, cost-effective, time-saving and ecoefficiency manufacturing techniques for batteries with outstanding microscopic size and aesthetic diversity. In this review, the state-of-the-art technologies and structural characteristics of printed SSBs have been comprehensively summarized and discussed, with a focus on the cutting-edge printing processes. Representative materials for fabricating printed electrodes and solid-state electrolytes (SSEs) have been systematically outlined, and performance optimization methods of printed SSBs through material modification have been discussed. Furthermore, this article highlights the design principles and adjustment strategies of printing processes of advanced SSB devices to realize high performance. Finally, the persistent challenges and potential opportunities are also highlighted and discussed, aiming to enlighten the future research for mass production of printed SSBs.
Electrocatalytic water splitting driven by renewable energy input to produce clean hydrogen (H2) has been widely considered a prospective approach for a future hydrogen-based society. However, the development of industrial alkaline water electrolyzers is hindered due to their unfavorable thermodynamics with high overpotential for delivering the whole process, caused by sluggish kinetics involving four-electron transfer. Further exploration of water electrolysis with low energy consumption and high efficiency is urgently required to meet the ever-growing energy storage and portfolio demands. This review emphasizes the strategies proposed thus far to pursue high-efficiency water electrolysis systems, including from the aspects of electrocatalysts (from monofunctional to bifunctional), electrode engineering (from powdery to self-supported), energy sources (from nonrenewable to renewable), electrolytes (from pure to hybrid), and cell configurations (from integrated to decoupled). Critical appraisals of the pivotal electrochemistry are highlighted to address the challenges in elevating the overall efficiency of water splitting. Finally, valuable insights for the future development directions and bottlenecks of advanced, sustainable, and high-efficiency water splitting systems are outlined.
The development of ordered Pt-based intermetallic compounds is an effective way to optimize the electronic characteristics of Pt and its disordered alloys, inhibit the loss of transition metal elements, and prepare fuel cell catalysts with high activity and long-term durability for the oxygen reduction reaction (ORR). This paper reviews the structure–activity characteristics, research advances, problems, and improvements in Pt-based intermetallic compound fuel cell catalysts for the ORR. First, the structural characteristics and performance advantages of Pt-based intermetallic compounds are analyzed and explained. Second, starting with 3d transition metals such as Fe, Co, and Ni, whose research achievements are common, the preparation process and properties of Pt-based intermetallic compound catalysts for the ORR are introduced in detail according to element types. Third, in view of preparation problems, improvements in the preparation processes of Pt-based intermetallic compounds are also summarized in regard to four aspects: coating to control the crystal size, doping to promote ordering transformation, constructing a “Pt skin” to improve performance, and anchoring and confinement to enhance the interaction between the crystal and support. Finally, by analyzing the research status of Pt-based intermetallic compound catalysts for the ORR, prospective research directions are suggested.
In this paper the electrochemical properties of some platinum-based nanoalloys are reviewed. The revision is centered on electrocatalytic materials generated via the carbonyl chemical route (CCR). In considering the effects of segregation in these bimetals, the reaction of the hydrogen oxidation (HOR) and oxygen reduction (ORR) in the alkaline medium was investigated. The reaction kinetics of these electrochemical processes in the alkaline electrolyte is still a challenge. For the design of high-performance platinum-based electrocatalysts, it is of importance to know that the kinetics of HOR and ORR also depends on the Pt adsorbate. The electrochemical analysis, based on the study of Pt nanoalloyed surfaces with different Pt-adsorbate interactions, was taken into account. A clear trend in the HOR as well as the ORR activity, in the alkaline electrolyte, was established, revealing that the activity changes in the order PtSn/C < PtCr/C < Pt/C (JM) < PtCo/C < PtNi/C for the former, and for the latter Pt/C (Tek) < Pt/C (JM) < PtCr/C < PtNi/C. The decisive effect of the Pt-Had energy on the HOR kinetics on Pt surfaces apparently depends on the oxophilicity role of the metal to favor M-OHad. The apparent electronic effect is not evident on these materials, except if a strong metal interaction is induced per se with either the carbon or oxide supports, e.g., the Pt/SnO2-C interface in acidic media. Favorable effects of Pt-Had energy on HOR kinetics were found with the oxophilicity of the sp2 domains of carbon that serve as anchoring or nucleation sites for platinum atoms. These results were compared with the literature data, and it turns out that this type of strong metal support interaction (SMSI) modification is favorably induced by UV–VIS irradiation and outperforms Pt-M materials to some extent. Either for HOR or ORR, it is shown that non-noble metals not only act as a surrogate metal for Pt utilization by inducing a compressive stress effect between the Pt atoms in the outermost layer but also participate in the electrocatalytic reaction. This information is important to understand and develop structures with the Pt/C catalyst for the manufacture of electrode materials in the alkaline medium.
Flexible and free-standing electrospun nanofibres have been used as electrode materials in electrochemical energy storage systems due to their versatile properties, such as mechanical stability, superb electrical conductivity, and high functionality. In energy storage systems such as metal-ion, metal-air, and metal-sulphur batteries, electrospun nanofibres are vital for constructing flexible electrodes and substantially enhancing their electrochemical properties. The need for flexible batteries has increased with increasing demand for new products such as wearable and flexible devices, including smartwatches and flexible displays. Conventional batteries have several semirigid to rigid components that limit their expansion in the flexible device market. The creation of flexible and wearable batteries with greater mechanical flexibility, higher energy, and substantial power density is critical in meeting the demand for these new electronic items. The implementation of carbon and carbon-derived composites into flexible electrodes is required to realize this goal. It is essential to understand recent advances and the comprehensive foundation behind the synthesis and assembly of various flexible electrospun nanofibres. The design of nanofibres, including those comprising carbon, N-doped carbon, hierarchical, porous carbon, and metal/metal oxide carbon composites, will be explored. We will highlight the merits of electrospun carbon flexible electrodes by describing porosity, surface area, binder-free and free-standing electrode construction, cycling stability, and performance rate. Significant scientific progress has been achieved and logistical challenges have been met in promoting secondary battery usage; therefore, this review of flexible electrode materials will advance this easily used and sought-after technology. The challenges and prospects involved in the timely development of carbon nanofibre composite flexible electrodes and batteries will be addressed.
All-solid-state batteries (ASSBs) with solid-state electrolytes and lithium-metal anodes have been regarded as a promising battery technology to alleviate range anxiety and address safety issues due to their high energy density and high safety. Understanding the fundamental physical and chemical science of ASSBs is of great importance to battery development. To confirm and supplement experimental study, theoretical computation provides a powerful approach to probe the thermodynamic and kinetic behavior of battery materials and their interfaces, resulting in the design of better batteries. In this review, we assess recent progress in the theoretical computations of solid electrolytes and the interfaces between the electrodes and electrolytes of ASSBs. We review the role of theoretical computation in studying the following: ion transport mechanisms, grain boundaries, phase stability, chemical and electrochemical stability, mechanical properties, design strategies and high-throughput screening of inorganic solid electrolytes, mechanical stability, space-charge layers, interface buffer layers and dendrite growth at electrode/electrolyte interfaces. Finally, we provide perspectives on the shortcomings, challenges and opportunities of theoretical computation in regard to ASSBs.
Lithium-metal batteries with high energy/power densities have significant applications in electronics, electric vehicles, and stationary power plants. However, the unstable lithium-metal-anode/electrolyte interface has induced insufficient cycle life and safety issues. To improve the cycle life and safety, understanding the formation of the solid electrolyte interphase (SEI) and growth of lithium dendrites near the anode/electrolyte interface, regulating the electrodeposition/electrostripping processes of Li+, and developing multiple approaches for protecting the lithium-metal surface and SEI layer are crucial and necessary. This paper comprehensively reviews the research progress in SEI and lithium dendrite growth in terms of their classical electrochemical lithium plating/stripping processes, interface interaction/nucleation processes, anode geometric evolution, fundamental electrolyte reduction mechanisms, and effects on battery performance. Some important aspects, such as charge transfer, the local current distribution, solvation, desolvation, ion diffusion through the interface, inhibition of dendrites by the SEI, additives, models for dendrite formation, heterogeneous nucleation, asymmetric processes during stripping/plating, the host matrix, and in situ nucleation characterization, are also analyzed based on experimental observations and theoretical calculations. Several technical challenges in improving SEI properties and reducing lithium dendrite growth are analyzed. Furthermore, possible future research directions for overcoming the challenges are also proposed to facilitate further research and development toward practical applications.
Sunlight is the most abundant and inexhaustible energy source on earth. However, its low energy density, dispersibility and intermittent nature make its direct utilization with industrial relevance challenging, suggesting that converting sunlight into chemical energy and storing it is a valuable measure to achieve global sustainable development. Carbon–neutral, clean and secondary pollution-free solar-driven water splitting to produce hydrogen is one of the most attractive avenues among all the current options and is expected to realize the transformation from dependence on fossil fuels to zero-pollution hydrogen. Artificial photosynthetic systems (APSs) based on photoelectrochemical (PEC) devices appear to be an ideal avenue to efficiently achieve solar-to-hydrogen conversion. In this review, we comprehensively highlight the recent developments in photocathodes, including architectures, semiconductor photoabsorbers and performance optimization strategies. In particular, frontier research cases of organic semiconductors, dye sensitization and surface grafted molecular catalysts applied to APSs based on frontier (molecular) orbital theory and semiconductor energy band theory are discussed. Moreover, research advances in typical photoelectrodes with the metal–insulator–semiconductor (MIS) architecture based on quantum tunnelling are also introduced. Finally, we discuss the benchmarks and protocols for designing integrated tandem photoelectrodes and PEC systems that conform to the solar spectrum to achieve high-efficiency and cost-effective solar-to-hydrogen conversion at an industrial scale in the near future.
Li–air batteries are a promising type of energy storage technology because of the ultra-high theoretical specific energy. Great advances are made in recent years, including the illustration of reaction mechanisms, development of effective catalyst materials, and design of battery structures accelerating species transport. However, the application still suffers from low rate capability, poor round-trip efficiency, and unsatisfactory cycling life. Herein, we mainly focus on the species transport issues of non-aqueous Li–air batteries, including Li+ across the solid surfaces and the electrolyte, O2 solubility and diffusivity, distribution of intermediates and products, and side reactions by other components from the air. Besides, considerable emphasis is paid to expound the approaches for enhancing species transport and accelerating reactions, among which the realization of well-designed electrode structures and flowing electrolytes is of great significance for the rapid migration of O2 and Li+ and mitigating the negative effects by solid insoluble Li2O2. Moreover, optimizing reaction interfaces and operating conditions is an attractive alternative to promote reaction rates. This work aims to identify the mechanism of transport issues and corresponding challenges and perspectives, guiding the structure design and material selection to achieve high-performance Li–air batteries.
Solid-state lithium-metal batteries (SLMBs) have been regarded as one of the most promising next-generation devices because of their potential high safety, high energy density, and simple packing procedure. However, the practical applications of SLMBs are restricted by a series of static and dynamic interfacial issues, including poor interfacial contact, (electro-)chemical incompatibility, dynamic Li dendrite penetration, etc. In recent years, considerable attempts have been made to obtain mechanistic insight into interfacial failures and to develop possible strategies towards excellent interfacial properties for SLMBs. The static and dynamic failure mechanisms at interfaces between solid electrolytes (SEs) and electrodes are comprehensively summarized, and design strategies involving interfacial modification, electrode/SE engineering, and the monolithic construction of SLMBs are discussed in detail. Finally, possible research methodologies such as theoretical calculations, advanced characterization techniques, and versatile design strategies are provided to tackle these interfacial problems.
Catalyst layer (CL) is the core component of proton exchange membrane (PEM) fuel cells, which determines the performance, durability, and cost. However, difficulties remain for a thorough understanding of the CLs’ inhomogeneous structure, and its impact on the physicochemical and electrochemical properties, operating performance, and durability. The inhomogeneous structure of the CLs is formed during the manufacturing process, which is sensitive to the associated materials, composition, fabrication methods, procedures, and conditions. The state-of-the-art visualization and characterization techniques are crucial to examine the CL structure. The structure-dependent physicochemical and electrochemical properties are then thoroughly scrutinized in terms of fundamental concepts, theories, and recent progress in advanced experimental techniques. The relation between the CL structure and the associated effective properties is also examined based on experimental and theoretical findings. Recent studies indicated that the CL inhomogeneous structure also strongly affects the performance and degradation of the whole fuel cell, and thus, the interconnection between the fuel cell performance, failure modes, and CL structure is comprehensively reviewed. An analytical model is established to understand the effect of the CL structure on the effective properties, performance, and durability of the PEM fuel cells. Finally, the challenges and prospects of the CL structure-associated studies are highlighted for the development of high-performing PEM fuel cells.
Carbonaceous materials for lithium (Li)/sodium (Na)-ion batteries have attracted significant attention because of their widespread availability, renewable nature, and low cost. During the past decades, although great efforts have been devoted to developing high-performance carbonaceous materials with high capacity, long life span, and excellent rate capability, the low initial Coulombic efficiency (ICE) of high-capacity carbonaceous materials seriously limits their practical applications. Various methods have been successfully exploited, and a revolutionary impact has been achieved through the utilization of different techniques. Different carbonaceous materials possess different ion storage mechanisms, which means that the initial capacity loss may vary. However, there has rarely been a special review about the origins of and progress in the ICE for carbonaceous materials from the angle of the crystal structure. Hence, in this review, the structural differences between and ion storage mechanisms of various carbonaceous materials are first introduced. Then, we deduce the correlative factors of low ICE and thereafter summarize the proposed strategies to address these issues. Finally, some challenges, perspectives, and future directions on the ICE of carbonaceous materials are given. This review will provide deep insights into the challenges of improving the ICE of carbonaceous anodes for high-energy Li/Na-ion batteries, which will greatly contribute to their commercialization process.
Carbonaceous materials for lithium (Li)/sodium (Na)-ion batteries have attracted significant attention because of their widespread availability, renewable nature, and low cost. During the past decades, although great efforts have been devoted to developing high-performance carbonaceous materials with high capacity, long life span, and excellent rate capability, nevertheless the low initial Coulombic efficiency (ICE) of high capacity carbonaceous materials seriously limits their practical applications. Various methods have been successfully exploited and a revolutionary impact has been achieved through the utilization of different techniques. It is well known that different carbonaceous materials possess different ion storage mechanisms, which means the initial capacity loss may vary. However, there has rarely been a special review about the origins and progress of ICE for carbonaceous materials from the angle of crystal structure. Hence, in this review, the structural differences and ion storage mechanisms between various carbonaceous materials are particularly introduced firstly. And then, we conclude the correlative factors of low ICE, and thereafter summarize the proposed strategies to address these issues. Finally, some challenges, perspectives, and future directions on the ICE of carbonaceous materials have been given. This review will provide deep insights into the challenges of improving the ICE of carbonaceous anodes for high-energy Li/Na-ion batteries, which will greatly contribute to their commercialization process.
MXenes have attracted increasing attention because of their rich surface functional groups, high electrical conductivity, and outstanding dispersibility in many solvents, and have demonstrated competitive efficiency in energy storage and conversion applications. However, the restacking nature of MXene nanosheets like other two-dimensional (2D) materials through van der Waals forces results in sluggish ionic kinetics, restricted number of active sites, and ultimate deterioration of MXene material/device performance. The strategy of raising 2D MXenes into three-dimensional (3D) structures has been considered an efficient way for reducing restacking, providing greater porosity, higher surface area, and shorter distances for mass transport of ions, surpassing standard one-dimensional (1D) and 2D structures. In multivalent ion batteries, the positive multivalent ions combine with two or more electrons at the same time, so their capacities are two or three times that of lithium-ion batteries (LIBs) under the same conditions, e.g., a magnesium ion battery has a high theoretical specific capacity of 2 205 mAh g−1 and a high volumetric capacity of 3 833 mAh cm−3. In this review, we summarize the most recent strategies for fabricating 3D MXene architectures, such as assembly, template, 3D printing, electrospinning, aerogel, and gas foaming methods. Special consideration has been given to the applications of highly porous 3D MXenes in energy storage devices beyond LIBs, such as sodium ion batteries (SIBs), potassium ion batteries (KIBs), magnesium ion batteries (MIBs), zinc ion batteries (ZIBs), and aluminum ion batteries (AIBs). Finally, the authors provide a summary of the future opportunities and challenges for the construction of 3D MXenes and MXene-based electrodes for applications beyond LIBs.
Rechargeable all-solid-state batteries (ASSBs) are considered to be the next generation of devices for electrochemical energy storage. The development of solid-state electrolytes (SSEs) is one of the most crucial subjects in the field of energy storage chemistry. The newly emerging halide SSEs have recently been intensively studied for application in ASSBs due to their favorable combination of high ionic conductivity, exceptional chemical and electrochemical stability, and superior mechanical deformability. In this review, a critical overview of the development, synthesis, chemical stability and remaining challenges of halide SSEs is given. The design strategies for optimizing the ionic conductivity of halide SSEs, such as element substitution and crystal structure design, are summarized in detail. Moreover, the associated chemical stability issues in terms of solvent compatibility, humid air stability and corresponding degradation mechanisms are discussed. In particular, advanced in situ/operando characterization techniques applied to halide-based ASSBs are highlighted. In addition, a comprehensive understanding of the interface issues, cost issues, and scalable processing challenges faced by halide-based ASSBs for practical application is provided. Finally, future perspectives on how to design high-performance electrode/electrolyte materials are given, which are instructive for guiding the development of halide-based ASSBs for energy conversion and storage.
In this review, a critical overview is given on the development, synthesis, chemical stability and remaining challenges facing for halide SSEs. The design strategies for optimizing ionic conductivity of halide SSEs like elements substitution, crystal structures design are summarized in detail. Future perspectives are given on how to design high-performance electrode/electrolyte materials.
Owing to the advantages of high energy density and environmental friendliness, lithium-ion batteries (LIBs) have been widely used as power sources in electric vehicles, energy storage systems and other devices. Conventional LIBs composed of liquid electrolytes (LEs) have potential safety hazards; thermal runaway easily leads to battery explosion and spontaneous combustion. To realize a large-scale energy storage system with higher safety and higher energy density, replacing LEs with solid-state electrolytes (SSEs) has been pursued. Among the many SSEs, sulfide SSEs are attractive because of their high ionic conductivities, easy processabilities and high thermostabilities. However, interfacial issues (interfacial reactions, chemomechanical failure, lithium dendrite formation, etc.) between sulfide SSEs and electrodes are factors limiting widespread application. In addition, the intrinsic interfacial issues of sulfide SSEs (electrochemical windows, diffusion mechanisms of Li+, etc.) should not be ignored. In this review, the behaviors, properties and mechanisms of interfaces in all-solid-state lithium batteries with a variety of sulfide SSEs are comprehensively summarized. Additionally, recent research progress on advanced characterization methods and designs used to stabilize interfaces is discussed. Finally, outlooks, challenges and possible interface engineering strategies are analyzed and proposed.
Two-dimensional (2D) mesoporous materials (2DMMs), defined as 2D nanosheets with randomly dispersed or orderly aligned mesopores of 2–50 nm, can synergistically combine the fascinating merits of 2D materials and mesoporous materials, while overcoming their intrinsic shortcomings, e.g., easy self-stacking of 2D materials and long ion transport paths in bulk mesoporous materials. These unique features enable fast ion diffusion, large specific surface area, and enriched adsorption/reaction sites, thus offering a promising solution for designing high-performance electrode/catalyst materials for next-generation energy storage and conversion devices (ESCDs). Herein, we review recent advances of state-of-the-art 2DMMs for high-efficiency ESCDs, focusing on two different configurations of in-plane mesoporous nanosheets and sandwich-like mesoporous heterostructures. Firstly, a brief introduction is given to highlighting the structural advantages (e.g., tailored chemical composition, sheet configuration, and mesopore geometry) and key roles (e.g., active materials and functional additives) of 2DMMs for high-performance ESCDs. Secondly, the chemical synthesis strategies of 2DMMs are summarized, including template-free, 2D-template, mesopore-template, and 2D mesopore dual-template methods. Thirdly, the wide applications of 2DMMs in advanced supercapacitors, rechargeable batteries, and electrocatalysis are discussed, enlightening their intrinsic structure–property relationships. Finally, the future challenges and perspectives of 2DMMs in energy-related fields are presented.
In this review, the recent advances of 2DMMs (including in-plane mesoporous nanosheets and sandwich-like mesoporous heterostructures) for energy storage and conversion are systematically summarized.
Lithium-manganese-oxides have been exploited as promising cathode materials for many years due to their environmental friendliness, resource abundance and low biotoxicity. Nevertheless, inevitable problems, such as Jahn-Teller distortion, manganese dissolution and phase transition, still frustrate researchers; thus, progress in full manganese-based cathode materials (FMCMs) has been relatively slow and limited in recent decades. Recently, with the fast growth of vehicle electrification and large-scale energy-storage grids, there has been an urgent demand to develop novel FMCMs again; actually, new waves of research based on FMCMs are being created. Herein, we systematically review the history of FMCMs, correctly describe their structures, evaluate the advantages and challenges, and discuss the resolution strategies and latest developments. Additionally, beyond FMCMs, a profound discussion of current controversial issues, such as oxygen redox reaction, voltage decay and voltage hysteresis in Li2MnO3-based cathode materials, is also presented. This review summarizes the effectively optimized approaches and offers a few new possible enhancement methods from the perspective of the electronic-coordination-crystal structure for building better FMCMs for next-generation lithium-ion batteries.