Showing papers in "Advanced Energy Materials in 2019"

Triboelectric Nanogenerator: A Foundation of the Energy for the New Era

Abstract: The triboelectric effect is ubiquitous in our everyday life and results from two different materials coming into contact. It is generally regarded as a negative effect in industry given that the electrostatic charges induced from it can lead to ignition, dust explosions, dielectric breakdown, electronic damage, etc. From an energy point of view, those electrostatic charges constitute a capacitive energy device when the two triboelectric surfaces are separated, which led to the invention of early electrostatic generators such as the “friction machine” and Van de Graaff generator.[1] As the world is marching into the era of the internet of things (IoTs) and artificial intelligence, the most vital development for hardware is a multifunctional array of sensing systems, which forms the foundation of the fourth industrial revolution toward an intelligent world. Given the need for mobility of these multitudes of sensors, the success of the IoTs calls for distributed energy sources, which can be provided by solar, thermal, wind, and mechanical triggering/vibrations. The triboelectric nanogenerator (TENG) for mechanical energy harvesting developed by Z.L. Wang’s group is one of the best choices for this energy for the new era, since triboelectrification is a universal and ubiquitous effect with an abundant choice of materials. The development of self-powered active sensors enabled by TENGs is revolutionary compared to externally powered passive sensors, similar to the advance from wired to wireless communication. In this paper, the fundamental theory, experiments, and applications of TENGs are reviewed as a foundation of the energy for the new era with four major application fields: micro/nano power sources, self-powered sensors, large-scale blue energy, and direct high-voltage power sources. A roadmap is proposed for the research and commercialization of TENG in the next 10 years.

Energy Storage Data Reporting in Perspective—Guidelines for Interpreting the Performance of Electrochemical Energy Storage Systems

Abstract: Due to the tremendous importance of electrochemical energy storage, numerous new materials and electrode architectures for batteries and supercapacitors have emerged in recent years. Correctly characterizing these systems requires considerable time, effort, and experience to ensure proper metrics are reported. Many new nanomaterials show electrochemical behavior somewhere in between conventional double‐layer capacitor and battery electrode materials, making their characterization a non‐straightforward task. It is understandable that some researchers may be misinformed about how to rigorously characterize their materials and devices, which can result in inflation of their reported data. This is not uncommon considering the current state of the field nearly requires record breaking performance for publication in high‐impact journals. Incorrect characterization and data reporting misleads both the materials and device development communities, and it is the shared responsibility of the community to follow rigorous reporting methodologies to ensure published results are reliable to ensure constructive progress. This tutorial aims to clarify the main causes of inaccurate data reporting and to give examples of how researchers should proceed. The best practices for measuring and reporting metrics such as capacitance, capacity, coulombic and energy efficiencies, electrochemical impedance, and the energy and power densities of capacitive and pseudocapacitive materials are discussed.

Smart Windows: Electro-, Thermo-, Mechano-, Photochromics, and Beyond

Abstract: Smart window refers to the on-demand window that can dynamically modulate light transmittance. It is recognized as a promising technology to economize building energy A smart window that dynamically modulates light transmittance is crucial for building energy efficiently, and promising for on-demand optical devices. The rapid development of technology brings out different categories that have fundamentally different transmittance modulation mechanisms, including the electro-, thermo-, mechano-, and photochromic smart windows. In this review, recent progress in smart windows of each category is overviewed. The strategies for each smart window are outlined with particular focus on functional materials, device design, and performance enhancement. The advantages and disadvantages of each category are summarized, followed by a discussion of emerging technologies such as dual stimuli triggered smart window and integrated devices toward multifunctionality. These multifunctional devices combine smart window technology with, for example, solar cells, triboelectric nanogenerators, actuators, energy storage devices, and electrothermal devices. Lastly, a perspective is provided on the future development of smart windows. Smart Windows

Shape Conformal and Thermal Insulative Organic Solar Absorber Sponge for Photothermal Water Evaporation and Thermoelectric Power Generation

Abstract: DOI: 10.1002/aenm.201900250 can attain the highest achievable conversion efficiency and enable a broad range of applications, including domestic heating, brine desalination, wastewater purification, steam sterilization, and power generation.[1–7] One actualization of solarto-thermal technology, solar-driven water evaporation can directly transfer heat to drive evaporation using sunlight as the only power input.[8–15] Compared with the conventional solar-driven steam generation system which requires high optical devices and large footprints investment, the emerging interfacial photothermal water evaporation based on nanostructured solar receiver materials restrict the solar heat at the water–air interface to suppress the heat losses and enhance the conversion efficiency. To date, significant progress in preparation of solar absorber materials, including semiconductors,[16–18] metallic,[19–21] and carbonaceous nanomaterials,[22–25] alongside with prudent system designs, e.g., environmental enhancement,[26–28] optical,[28–30] and thermal management[31–33] have been made to improve solar energy conversion efficiency. However, extended and collaborative utilization of nonconcentrated solar energy conversion for practical applications is making a little headway due to inconsequential/conflicting outcomes. On one hand, the heat losses from the solar absorber to bulk water and surrounding air for water vaporization are inevitable. On the other hand, constructive low-grade solar heat harvesting during evaporation are rarely reported. Therefore, effective thermal management and synergic utilization of the solar steam generation are essential. Another major roadblock toward photothermal technological advancement is the accessibility to a robust and practical material structure for practical deployment. As such, lightweight, load bearing, weather resistant, and uncommonly shape adaptive solar absorber materials are long sought after for durable outdoor application. Herein, we report a 3D organic bucky sponge that is collectively elastic, broadband light absorbing, and heat insulative that enables desired combination of efficient solar thermal conversion and mechanical stability. The 3D cellular truss is highly compressible and elastic which assumes excellent shape conformity and recovery, particularly beneficial to maximize space usage as well as for flexible, resilient outdoor purposes. Importantly, a rational integration of efficient solar water Solar-driven interfacial vaporization by localizing solar-thermal energy conversion to the air–water interface has attracted tremendous attention due to its high conversion efficiency for water purification, desalination, energy generation, etc. However, ineffective integration of hybrid solar thermal devices and poor material compliance undermine extensive solar energy exploitation and practical outdoor use. Herein, a 3D organic bucky sponge that has a combination of desired chemical and physical properties, i.e., broadband light absorbing, heat insulative, and shape-conforming abilities that render efficient photothermic vaporization and energy generation with improved operational durability is reported. The highly compressible and readily reconfigurable solar absorber sponge not only places less constraints on footprint and shape defined fabrication process but more importantly remarkably improves the solar-to-vapor conversion efficiency. Notably, synergetic coupling of solar-steam and solar-electricity technologies is realized without trade-offs, highlighting the practical consideration toward more impactful solar heat exploitation. Such solar distillation and low-grade heat-to-electricity generation functions can provide potential opportunities for fresh water and electricity supply in off-grid or remote areas.

Uniform High Ionic Conducting Lithium Sulfide Protection Layer for Stable Lithium Metal Anode

Abstract: DOI: 10.1002/aenm.201900858 dendrites,[6] guided lithium plating,[7] and nanostructured electrode design.[8] Among all the methods, the focus on solidelectrolyte interphase (SEI) between anode materials and electrolyte is one of the most critical issues. During LMB operation, the SEI that primarily originated from electrolyte decomposition, is easily cracked. This will locally enhance ion flux and promote nonuniform lithium depositing/stripping,[9] resulting in Li dendrites that can trigger internal short circuit and compromise battery safety. Repeated breakdown and repair of SEI during cycling create a vicious cycle which alternates between “uneven stripping/plating and SEI fracture,” brings about continuous loss of active materials and limited battery cycle life. Therefore, an ideal SEI should continuously passivate the anode and prevent the parasitic reactions between reactive anode and electrolyte to address the aforementioned problems in principle.[3] Previous studies have demonstrated several effective artificial SEI to protect lithium metal anode such as polymer,[10] inorganic conductive compounds,[11,12] electrolyte additives,[13,14] and carbonbased materials.[7,15] However, the evolution of SEI during cycling and key mechanisms such as impact of SEI quality on its stability need to be further explored.[16] Herein, we demonstrate a “simultaneous homogeneous and high ionic conductivity” strategy by developing a method of forming a uniform lithium sulfide (Li2S) protective layer for suppressing dendrite growth and stabilizing the lithium metal anode. Although Li2S interfacial layers through soluble electrolyte additives have been studied before,[14,17–20] the work here demonstrates that the elevated temperature (170 °C) and gas phase reaction are critical for the synthesis of a homogenous Li2S coating, which importantly can be used as SEI in carbonate electrolyte system. We reveal the evolution of thus formed Li2S artificial SEI component distribution during battery operation: the uniform and high ionic conductivity protective layer turns into a layered SEI that preserves protective function, rather than into a disordered, broken SEI mainly made up of parasitic reaction products. Simulation results also confirm the critical importance of compositional homogeneity and high ionic conductivity in stabilizing SEI. With this strategy, stable cycles in both high capacity symmetric cells and Li–LiFePO4 full cells were realized. We believe that this practical fabrication method, fundamental design strategy, and understanding on Artificial solid-electrolyte interphase (SEI) is one of the key approaches in addressing the low reversibility and dendritic growth problems of lithium metal anode, yet its current effect is still insufficient due to insufficient stability. Here, a new principle of “simultaneous high ionic conductivity and homogeneity” is proposed for stabilizing SEI and lithium metal anodes. Fabricated by a facile, environmentally friendly, and low-cost lithium solidsulfur vapor reaction at elevated temperature, a designed lithium sulfide protective layer successfully maintains its protection function during cycling, which is confirmed by both simulations and experiments. Stable dendritefree cycling of lithium metal anode is realized even at a high areal capacity of 5 mAh cm−2, and prototype Li–Li4Ti5O12 cell with limited lithium also achieves 900 stable cycles. These findings give new insight into the ideal SEI composition and structure and provide new design strategies for stable lithium metal batteries.