Accounts of Materials Research

ConspectusAll-solid-state lithium batteries have received considerable attention in recent years with the ever-growing demand for efficient and safe energy storage technologies. However, key issues remain unsolved and hinder full-scale commercialization of all-solid-state lithium batteries. Previously, most discussion only focused on how to achieve high energy density from the theoretical perspective. Herein, we analyze the real cases of different kinds of all-solid-state lithium batteries with high energy density to understand the current status, including all-solid-state lithium-ion batteries, all-solid-state lithium metal batteries, and all-solid-state lithium–sulfur batteries. First, we propose a general calculation method to visually compare the above battery systems partly due to no normative parameters for solid-state batteries. After then, we discuss and interpret the key parameters and current situation of all-solid-state lithium batteries. Through the summary and analysis of the frontier, one can find that, although some breakthrough has been made in energy density and areal capacity for solid-state batteries, there are still many aspects to be improved such as power density and rate performance. Therefore, in response to the challenges, we propose possible directions for future development, including the ways to prepare different kinds of solid electrolyte films to reduce the proportion of inactive substances in the cell. The advantages and disadvantages are discussed about three typical solid-state electrolyte films (inorganic solid electrolyte, solid polymer electrolyte, and composite solid electrolyte). In addition, potential candidate anodes with high capacity and cathodes with high voltage and/or high capacity are also discussed in details. The combination of lithium metal anodes with ultrahigh capacity and cathodes with both high capacity and high voltage is the current mainstream direction. However, the interface problems have become the most pressing factor on the application. Therefore, we introduce the origin of interfaces and interphases and discuss how to build a stable electrode/solid electrolyte interface. One thing is clear that artificial solid electrolyte interphases and composite solid electrolytes are effective to obtain stable anode/solid electrolyte interfaces, which can prevent lithium from constantly reacting with solid electrolytes, ensure the uniform lithium deposition and prevent the formation of lithium dendrites. For the cathode/solid electrolyte interface, reasonable composite cathodes, multilayer design, and composite solid electrolytes can optimize the electrode and interface for stable cycles at high voltages and high current densities. Furthermore, the contribution of high-throughput computations and machine learning is introduced in accelerating materials screening and development. Among them, progress has been made in solid electrolytes and artificial solid electrolyte interphases through materials genome engineering and machine learning. Finally, we provide some outlook for the future development. We hope that this Account could help understand the current status and inspire more future breakthrough for all-solid-state lithium batteries.

Junwu Sang

Bin Tang

Kecheng Pan

Yan-Bing He

Zhen Zhou

Acc. Mater. Res.

Current Status and Enhancement Strategies for All-Solid-State Lithium Batteries

全固态锂电池的现状与增强策略

Jia Lv

Xun Liu

Lichen Yin

Yiyun Cheng

Rational Engineering of Cytosolic Delivery Systems for Protein Therapeutics

蛋白质治疗药物的细胞质递送系统的合理工程

ConspectusRecent decades have witnessed the rapid development of catalytic science, especially after Taylor and Armstrong proposed the notion of the “active site” in 1925. By optimizing reaction paths and reducing the activation energies of reactions, catalysts appear in more than 90% of chemical production reactions, involving homogeneous catalysis, heterogeneous catalysis, and enzyme catalysis. Because of the 100% efficiency of active atom utilization and the adjustable microenvironment of metal centers, single-atom catalysts (SACs) shine in various catalytic fields for enhancing the rate, conversion, and selectivity of chemical reactions. Nevertheless, a solo active site determines a fixed adsorption mode, and the adsorption energies of intermediates from multistep reactions linking with a solo metal site are related to each other. For a specific multistep reaction, it is almost impossible to optimally adjust the adsorption of every intermediate on the solo site simultaneously. This phenomenon is termed the scaling relationship limit (SRL) and is an unavoidable obstacle in the development of pure SACs.Dual-atom catalysts (DACs), perfectly inheriting the advantages of SACs, can exhibit better catalytic performance than simple SACs and thus have gradually gained researchers’ attention. Depending on the dual-metal structure, dual-metal sites (DMSs) in DACs can be divided into two separated heterometal sites, two linked homometal sites, and two linked heterometal sites. Two separated heterometal sites prescribe a distance limit between two metal sites for electron interaction. Currently, the active origins of DACs can be summarized in the following three points: (1) electronic effect, in which only one metal center serves as active site and the other plays an electronic regulatory role; (2) synergistic effect, in which two metal centers separately catalyze different core steps to improve catalytic performance together; (3) adsorption effect, in which offering additional sites changes the adsorption structures to break the SRL based on SACs. Among the three active origins, optimizing the adsorption structure of intermediates upon DMSs is one of the most effective technologies to boost the catalytic property of DACs on the basis of SACs. To date, few contributions have focused on the development of DACs in various heterogeneous catalysis environments, including O2 reduction reaction, O2 evolution reaction, H2 evolution reaction, CO2 reduction reaction, N2 reduction reaction, and other conversion reactions.In this Account, a summary of recent progress regarding DACs in heterogeneous catalysis will be presented. First, the evolution of DACs from an unpopular discovery to research hot spot is illustrated through a timeline. In the next section, the DACs are divided into three categories, and the potential active origins of DACs are revealed by comparison with SACs. In addition, the techniques for constructing DACs are systematically summarized, including preparation of carbonous, pyrolysis-free, noncarbon-supported, and complex-type DACs. Furthermore, the underlying active origins of DACs in specific energy- and environment-related reactions are introduced in detail with assistance of theoretical calculations. Finally, we affirm the contribution of DACs to catalysis, particularly heterogeneous electrocatalysis, and provide an outlook regarding the development direction for DACs by discussing the major challenges. It is anticipated that this Account can inspire researchers to propel the advance of DACs.

Longbin Li

Kai Yuan

Yiwang Chen

Breaking the Scaling Relationship Limit: From Single-Atom to Dual-Atom Catalysts

打破缩放关系极限：从单原子到双原子催化剂

Dawei Wang

Xiaohong Wang

Wei Rao

Precise Regulation of Ga-Based Liquid Metal Oxidation

基于镓的液态金属氧化的精确调控

ConspectusSelf-healing ability is one of the most attractive features of biological tissues, as it helps living creatures to recover physiological functions and prolongs their lifespans after unexpected injuries. Inspired by this feature, self-healing artificial polymers have been developed based on extrinsic and intrinsic designs since the 1950s. In particular, the intrinsic self-healing polymers have received enormous attention since 2001 because of their unlimited self-healing times and easy preparation. Therefore, many excellent works are reported, and our understanding of the self-healing polymer goes deeper and deeper. Self-healing is the process of the rejoining of the dynamic bonds/interactions. Therefore, the healing process involves two critical factors. One is the dynamic nature of dynamic bonds/interactions. The other is the high mobility of the polymer chains. However, the dynamic bonds/interactions are vulnerable to external forces and environmental stimuli because their bond energy is lower than that of the covalent bonds, which leads to several innate drawbacks of intrinsic self-healing polymers, such as poor mechanical properties (low fracture strength, low fracture strain, low modulus, and low fracture toughness) and poor resistance against the external environment (vulnerable to acid, alkali, or moisture). Also, since high chain mobility is also a prerequisite for intrinsic self-healing, most polymers cannot be healed in the glassy state where the polymer chains are frozen. Therefore, it is challenging to develop high-performance self-healing polymers, which not only possess high mechanical strength, toughness, and stability under ambient conditions or severe environments but also manifest high self-healing efficiency in the rubbery state or even in the glassy state. Therefore, how to overcome this challenge has become a hot topic in the field of self-healing polymers.To address the above problem, many high-performance self-healing polymers with high mechanical properties, high self-healing ability, or high environmental stability are published by using different strategies. These strategies are effective at enhancing the mechanical properties or increasing its environmental stability and are worth learning about. Our group has carried out some work in this field. In this Account, we highlight our works toward fabricating high-performance self-healing polymers. We summarize the high-performance self-healing polymers from three aspects: self-healing polymers with high mechanical properties (such as high toughness, tensile strength, stretchability, and modulus), glassy polymers capable of self-healing in the glassy state, and environmentally stable self-healing polymers. In particular, strategies based on tailoring molecular-level structure, condensed structure, and filler reinforcement are discussed in detail to construct self-healing polymers with high mechanical properties. Finally, the future development of intrinsic self-healing polymers is examined from the perspective of practical application and fundamental research.

Yan Peng

Shiyu Gu

Qi Wu

Zhengtian Xie

Jinrong Wu

High-Performance Self-Healing Polymers

高性能自修复聚合物

ConspectusEfficient photovoltaics (PV) require capturing and converting solar energy across a broad range of energy. Losses due to thermalization and sub-bandgap photons place, however, significant boundaries on the performance of solar cells. For conventional single-junction cells, the theoretical maximum power conversion efficiency is capped at 33%, a constraint known as the detailed balance limit. Realizing the full potential of PVs requires developing novel strategies to overcome this fundamental obstacle. This Account describes the photon-management capabilities of acenes and addresses these fundamental losses en-route toward enhancing PV performances.For high-energy photons that exceed the semiconductor's bandgap energy, singlet fission (SF) is a down-conversion pathway to mitigate thermalization losses. SF is a process in organic materials, in which a singlet excited state is split into two independent triplet excited states, effectively doubling the number of charge carriers. Pentacenes stand out among acenes due to their exergonic nature of SF. Numerous molecular pentacene dimers have been synthesized to elucidate the relationship between structure and enhancing SF efficiency.A broader light-harvesting range of SF materials is realized by covalently attaching complementary absorbing energy donors to set up energy donor–acceptor conjugates. Förster resonance energy transfer (FRET) is operative in these energy donor-acceptor conjugates, effectively extending the absorption of SF materials, as the energy donor efficiently transfers its absorbed excitation energy to the energy acceptor. Our studies on various binding motifs show that FRET efficiency depends not only on parameters like the energy donor–acceptor distance and spectral overlap but also on subtle factors such as the alignment of transition dipoles, which significantly affect the energy transfer dynamics and efficiency.Turning to low-energy photons, triplet–triplet annihilation up-conversion (TTA-UC) provides a means of light up-conversion and, thereby, the reduction of sub-bandgap losses. In TTA-UC, a singlet excited state that is potent enough to generate charge carriers is formed by combining two triplet excitons. It is effectively the reverse process of SF. The higher triplet energy of tetracene and an endergonic SF renders them highly effective for TTA-UC. We focus on various tetracene-based systems that maximize TTA-UC efficiency.Besides TTA-UC, two-photon absorption (TPA) is yet another mechanism to leverage below-bandgap photons. It is a nonlinear optical (NLO) process, and acenes reveal NLO properties that are essential for extending light absorption into the near-infrared and still powering SF. We demonstrate in our proof-of-concept studies how TPA further broadens the application potential of acenes for PV systems.The strategies outlined in this Account illustrate that acenes are valuable for addressing mechanistic losses in conventional solar cells. In the final section, we examine light storage following SF by means of interfacial electron transfer. Efficient charge-injection powered by SF materials still requires more research before being implemented in large-scale PV designs.Overall, the advances discussed in this Account not only highlight the pivotal role of acenes as model systems to investigate photon down- and up-conversion processes but also paint a promising picture that more efficient solar energy conversion schemes exceeding the detailed-balance limit can be realized by implementing these materials.

Phillip M. Greißel

Anna-Sophie Wollny

Yifan Bo

Dominik Thiel

René Weiß

Dirk M. Guldi

Molecular Acenes for Light Capture, Conversion, and Storage

用于光捕获、转换和存储的分子并四苯类化合物

ConspectusThe haptic sense captures information arising from the somatosensory system─the sensor system of the body excluding the eyes, ears, nose, and tongue. That is, it captures stimuli arising from the skin (i.e., touch) and from internal structures (i.e., the musculoskeletal system and internal organs). The field of research called haptics is concerned with understanding and manipulating this sense, often using engineered technology, and usually for creating novel or realistic touch sensations. Fundamental to every tactile interaction is an interface between the skin and a material. Given that essentially all material objects are composed of or covered in organic media, we reasoned that we, as organic materials scientists, might be able to contribute to the understanding of the sense of touch by manipulating material properties on the molecular scale. Over time, our research group acquired additional skills in electrical engineering and developed strong collaborations with cognitive and behavioral scientists. With a shared curiosity about the sense of touch, we made what we believe are original contributions to the field of haptics.Our approach is guided by a paradigm consisting of four layers from which hypotheses can be generated, experiments can be designed, and whose analytical techniques may be applied. The layers are (1) material composition, (2) material properties, (3) interfacial properties between the skin and the material, and (4) human perception. For example, a material may be composed of one part silicon and two parts oxygen (material composition), which leaves the surface terminated in dipoles and thus a high surface polarizability (material properties). These dipoles may then interact with the skin with a strong van der Waals interaction and high friction (interfacial properties). This friction may lead to stick–slip behavior and could possibly be perceived as fine texture or roughness, even if the surface is smooth (perception).Another useful organizing principle is that of active vs passive touch. That is, engaging with an object with intent vs having an object brush up against one's skin without expectation. In either case, the sensation perceived can be described as either fundamental (e.g., roughness, coldness, compliance, and slipperiness) or blended (e.g., wetness). Beginning with an example of how our approach can be used to understand active touch of a blended sensation, we show how polyacrylamide hydrogels can be tuned by adjusting both the mechanical compliance and thermal conductivity to elicit different levels of perceived wetness. We then show how a purpose-designed conductive polymer can render sensations of roughness in the context of a virtual reality simulation that operates by both passive and active modalities. Lastly, we demonstrate a form of haptic "holography" using the photoacoustic effect; that is, π-conjugated materials coated on the skin can render sensations of vibration (perceived passively) when exposed to pulsed light. Throughout this Account, we describe how control of materials can be used to elicit senses artificially for both fundamental knowledge and for the ultimate development of richer human–machine interfaces.

Laura L. Becerra

Nicholas B. Root

Robert S. Ramji

Romke Rouw

Darren J. Lipomi

Use of Materials Science to Understand Haptic Perception

利用材料科学理解触觉感知

João Marreiros

Yuxiang Wang

MinGyu Song

William J. Koros

Matthew J. Realff

Christopher W. Jones

Ryan P. Lively

Fiber Sorbents – A Versatile Platform for Sorption-Based Gas Separations

纤维吸附剂——基于吸附的气体分离的多功能平台

Woo Je Chang

Allison M. Green

Zarko Sakotic

Daniel Wasserman

Thomas M. Truskett

Delia J. Milliron

Plasmonic Metal Oxide Nanocrystals as Building Blocks for Infrared Metasurfaces

等离子体金属氧化物纳米晶体作为红外超表面的构建基块

ConspectusPiezoionic skin sensors are one kind of artificial electrical skin that can output sensing signals in response to external strain or stress stimulus with merits of flexibility, lightness, scalability, and high sensitivity. They have been emerging as an important platform in artificial intelligence, such as in smart healthcare, bionic robotics, and microelectromechanical systems. Piezoionic sensors are typically composed of an electrolyte laminated with symmetric electrodes and are based on ion migration and redistribution under a gradient strain or stress field. However, existing challenges significantly impede the sensing performance of piezoionic sensors, including the low electromechanical coupling efficiency of the electrode materials, instability of electrolyte materials, and strain-induced interface separation of sensor interfaces. In recent years, our group and collaborators have made attempts addressing the as-mentioned critical challenges in order to achieve flexible piezoionic sensors with satisfying performance for wearable smart applications. First, for the electromechanical coupling efficiency of electrode materials, we have developed various electrode materials with highly efficient ion storage and transfer, such as graphdiyne, quinone composites, and graphitic carbon nitride. These materials present superior electrical and mechanical properties with enhanced electromechanical coupling efficiency. Second, in order to improve the stability of electrolytes, especially in an air environment, we have developed ionogel electrolytes instead of conventional hydrogel electrolytes. Ionogels contain highly stable ionic liquids, which effectively improve the air stability of sensor electrolytes, and the sensing properties of devices are preserved even after several months. Third, with regard to sensor interface separation, we have engineered stable material interfaces for piezoionic sensors with elaborate structures. The as-designed tree-root-inspired interfaces show high mechanical stability under various flexible conditions, and the piezoionic sensors display negligible performance deterioration under thousands of bending cycles in an ambient environment. Finally, we have obtained flexible piezoionic sensors and studied their practical applications, such as wearable electronics, health monitoring, and smart detections. For example, we have realized the accurate detection of blood pressure based on an out-of-plane piezoionic mechanism. This innovative technique completely avoids the cuff issue that commercial sphygmomanometers have. Moreover, we have developed multifinger-touch piezoionic sensor arrays for effective braille recognition, which have the potential to eliminate communication barriers with sight-impaired people. Human voices can be easily differentiated by detecting vocal-cord vibrations based on captured sensing signals with obviously different patterns. This smart technique is promising for extended and applied use in virtual reality technology. Lastly, a perspective on existing challenges of piezoionic sensors is highlighted to set a clear direction for future research, including low-cost material synthesis, the mass production of flexible sensors, and healthcare sensor products.

Abbreviation	Acc. Mater. Res.
Journal Impact	13.89
Quartiles(Global)	MATERIALS SCIENCE, MULTIDISCIPLINARY(Q1)

ISSN	2643-6728
h-index	39

Publication Information	Publisher: American Chemical Society，Publishing cycle: ，Journal Type: journal，Open Access Journals: No
Basic data	Year of publication: 2020，Proportion of original research papers: 100.00%，Self Citation Rate:， Gold OA Rate: 3.07%

Accounts of Materials Research

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