Advances and mechanisms in polymer composites toward thermal conduction and electromagnetic wave absorption.

Recently, the need for miniaturization and high integration have steered a strong technical wave in developing (micro-)electronic devices. However, excessive amounts of heat may be generated during operation/charging, severely affecting device performance and leading to life/property loss. Benefiting from their low density, easy processing and low manufacturing cost, thermally conductive polymer composites have become a research hotspot to mitigate the disadvantage of excessive heat, with potential applications in 5G communication, electronic packaging and energy transmission. By far, the reported thermal conductivity coefficient (λ) of thermally conductive polymer composite is far from expectation. Deeper understanding of heat transfer mechanism is desired for developing next generation thermally conductive composites. This review holistically scopes current advances in this field, while giving special attention to critical factors that affect thermal conductivity in polymer composites as well as the thermal conduction mechanisms on how to enhance the λ value. This review covers critical factors such as interfacial thermal resistance, chain structure of polymer, intrinsic λ value of different thermally conductive fillers, orientation/configuration of nanoparticles, 3D interconnected networks, processing technology, etc. The applications of thermally conductive polymer composites in electronic devices are summarized. The existing problems are also discussed, new challenges and opportunities are prospected. 

A Roadmap Review of Thermally Conductive Polymer Composites: Critical Factors, Progress, and Prospects

The Development Trend of Graphene Derivatives

The rational electrode design is one of the most important ways to enhance the electrochemical properties of lithium-sulfur batteries (LSBs). In this contribution, we use Ni-embedded porous graphitic carbon fiber (PGCF@Ni) as the scaffold to construct a novel cathode and anode for LSBs. With the help of elaborate surface engineering, the constructed solid electrolyte interface (SEI)@Li/PGCF@Ni anodes can effectively restrain the growth of lithium dendrites during the cycle, exhibiting an ultralow overpotential of ∼10 mV for 2000 h at 1 mA cm-2/1 mA h cm-2. The underlying mechanism is further investigated by COMSOL Multiphysics simulations. Additionally, the PGCF@Ni/S cathode fabricated by the molten sulfurizing method manifests superior rate performance and stability. Ultimately, the assembled SEI@Li/PGCF@Ni||PGCF@Ni/S full battery exhibits prominent electrochemical property with a high capacity retention of about 77.9% after 600 cycles at 1 C. Such success at the performance improvement in LSBs may open up avenues toward other rational designs of high-quality electrodes in electrochemical energy storage.

Employing Ni-Embedded Porous Graphitic Carbon Fibers for High-Efficiency Lithium-Sulfur Batteries.

Templating strategies for 3D-structured thermally conductive composites: Recent advances and thermal energy applications

Li has garnered enormous attention for next‐generation Li metal batteries owing to its remarkable theoretical capacity. Unfortunately, as an anode, Li suffers from serious safety issues and fast capacity fading due to the formation of Li dendrites, which hinders the practical application of Li anode. Herein, a LiAlO2‐PVDF composite modification layer is fabricated on the surface of Li metal to enhance its stability and electrochemical performance. Benefitting from the synergetic effects of high Li+ conductivity, high Li+ transference number, excellent mechanical properties, superior chemical durability, and compactness of the modification layer, the LiAlO2‐PVDF@Li electrode delivers an ultra‐long lifespan and a high capacity retention rate in the LiAlO2‐PVDF@Li│LiFePO4 full cell. The proposed strategy provides a new alternative anode for Li metal batteries with high performance and scalable production.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/sus2.43

A facile, scalable, high stability Lithium metal anode

Polymers are usually considered thermal insulators; however, significant enhancements in thermal conductivity (k) have been observed in oriented fibers and films. Despite being advantageous in real‐world applications, extending the linear thermal‐transport advantage of polymers into the 3D space in bulk materials is still limited due to the spatially interfacial phonon‐conduction barriers. Herein, inspired by the structure of tropocollagen, it is discovered that weaving hierarchically arranged poly(p‐phenylene benzobisoxazole) (PBO) fibers with a spiral configuration into an epoxy matrix can yield a 3D continuous thermal pathway. This achieves both a through‐plane k of 10.85 W m−1 K−1 and an in‐plane k of 7.15 W m−1 K−1. Theoretical molecular simulations in combination with classical nonlinear modeling attribute the above spatially thermally conductive achievement to not only the hierarchical molecular, spiral and weaving structure of PBO, but also the noncrystalline chains that carry overlapping phonon density of states, thus thermally bridging adjacent high‐k crystals in the PBO fiber. Consequently, the interfacial thermal resistance among high‐k PBO crystals is suppressed to be on the order of 10−10 m2 K W−1 in both the through‐plane and in‐plane directions. Other advantages include being lightweight, mechanically strong, flexible, and non‐combustible. This material creates opportunities for organic polymers in high‐performance thermal management applications.

Tropocollagen‐Inspired Hierarchical Spiral Structure of Organic Fibers in Epoxy Bulk for 3D High Thermal Conductivity

Moisture–electric generator (MEG)‐based blue energy is widely studied. There is still a significant challenge in improving the power of the MEGs system and expanding its application in self‐powered electronic skin. Inspired by the structure of ferns, a biomimetic moisture–electric aerogel is designed to collect energy. Polyvinyl alcohol dendritic colloids act as “roots” and “stems” to provide support and channels to transport water molecules. Meanwhile, “leaf‐like” graphene oxide sheets generate electricity through direct interaction with water. Besides, based on the above biomimetic structure, this work further enhances the output performance of MEGs by increasing the specific surface area (120.4 m2 g−1) and introducing an ultra‐high ion density gradient (from −35 to +37 mV). Meanwhile, due to the excellent water absorption, the MEGs show good salt resistance and cyclic stability. By constructing unique biomimetic structures, ultra‐high ion density gradient, and regulating environmental conditions, a high‐performance MEG is obtained, including ultra‐high open‐circuit voltage (1.9 V) and short‐circuit current (82.5 µA), the industry‐leading power density among MEGs with continuous output is reported in the literature (22.55 µW cm−2). Besides, the MEGs can accurately respond to environmental and pressure changes, showing its application potential in self‐powered electronic skin.

Biomimetic Aerogel for Moisture‐Induced Energy Harvesting and Self‐Powered Electronic Skin

Lithiophilic hosts are confirmed to effectively enhance the electrochemical stability of lithium (Li) anodes, thereby guaranteeing the safe, practical application of Li metal as the anode in rechargeable Li-ion batteries. This study reveals a lithiophilic three-dimensional copper current collector (Ag@CF). Silver (Ag) nanoparticles were anchored on the surface of a skeleton of copper foam (CF) via a facile displacement reaction under ultrasonic conditions. The introduced Ag nanoparticle layer reduces the nucleation barrier of Li, leading to a homogeneous Li nucleation and plating. Simultaneously, porous Ag@CF provides the structural support and storage volume of the Li anode, eliminating its volume change in the process of plating/stripping. Benefiting from the above, the Ag@CF electrode shows a superior electrochemical performance in half-type cells (near 100% coulomb efficiency for 350 cycles at 1 mA cm−2). Composite electrodes (Li-Ag@CF) preloaded in the Ag@CF network deliver an ultra-long lifespan of over 1600 h with a low over-potential at 1 mA cm−2 in Li-Ag@CF symmetric cells. Furthermore, LiFePO4∣Li-Ag@CF full cells display enhanced capacity retention (over 80% for 800 cycles at 1 or 3 C). More importantly, this method is facile, large-scalable, and low-cost, which offers an alternation strategy for the practical application of stable Li anodes. 

/pdf/facile-lithiophilic-3d-copper-current-collector-for-stable-1qrg4rh6.pdf

Facile Lithiophilic 3D Copper Current Collector for Stable Li Metal Anode

Fe3O4@SiO2/PAM/Glycerol photonic crystal film as a long-term effective sensor for ambient humidity

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