The demand for sustainable green energy and quality of life has become more urgent as modern society and industry move forward at full speed. This has further promoted the shift of society to environmental and sustainable development. [1,2] The emergence of LIBs has greatly mitigated the major petroleum-fuel pollution and energy crises, and is also a good replacement for certain new energy sources, with uncertain characteristics and intermittent properties including tidal energy, solar, hydroelectric, nuclear, and wind power developed. [3] In the 1990s, Sony commercialized LIBs successfully. [1] Using their unique advances, including high power density, no storage, small size, light weight, long cycle life, and low self-discharge rates, LIBs have so far gathered enormous market share following 30 years of development and progress in the sector. [1,4] It is widely used in electronic consumer, medical, electric vehicle, the industry, aerospace and defense, power storage, and other industries. [5] Moreover, the battery market of lithium-ion is currently undergoing major changes and LIBs are expected to grow over hundreds of gigawatt hours per year worldwide in the next five years and to account for 70% of the battery rechargeable market in 2025. [6] The global demand for lithium batteries in 2018 is 231 326 billion Yuan and the volume of shipments is 146.38 GWh, according to the prediction of the relevant research institutions of the industry. The demand for the market in lithium batteries is going to reach 694 265 billion yuan in particular, with a market capacity of 439.32 GWh in 2025. Driven by the continuous electrification of the auto industry, LIBs have reached millions of trading volumes as the main driver of electric vehicles and hybrid vehicles will continue to grow in the future. [7,8] The global market for LIBs is estimated to be around US $40 billion by 2025, and more than a third is expected to come from the hybrid and electric vehicle markets. [9] In the face of these massive volumes of LIBs, all demands have promoted the production of a large number of LIBs, which have led to large production shortages, in particular metal resources such as lithium and cobalt. [10,11] LIBs in electric vehicles have a life span of only 5-10 years, while small electronic products have a lifetime almost 3 years. [12,13] Therefore, in the face of the explosive growth and of such a substantial amount of rechargeable LIBs, generous LIBs will be scrapped in the immediate future. It is speculated that China alone can produce 500 000 metric tons of used LIBs in 2020, and the world is expected to process 11 million tons of spent LIBs by 2030. [12,14] However, the high metal content of waste LIB is an important metal resource, especially because global reserves are limited to approximately 62 million tons of Li and 145 million tons of Co. The supply of these raw materials from natural resources will not be able to meet future demand.

Ultraflexible and degradable organic synaptic transistors (OSTs) enable seamless integration with the human body and are capable of disintegrating after completing their specific functions, opening up remarkable new opportunities for “green” electronics in implantable neuromorphic systems, brain‐computer interfaces and wearable artificial intelligence systems. However, it is still an outstanding challenge to realize such synaptic transistors that simultaneously satisfy both ultra flexibility and degradability. The advancement of such electronics critically hinges on the development of ultraflexible and degradable gate dielectrics, which is the vital component to realize synaptic function of transistors. Here, for the first time, a self‐supporting natural dextran membrane is utilized as the gate dielectric to achieve an ultraflexible and degradable OST. The resultant device is only 309 nm thick, and can maintain stable synaptic behavior on various curved surfaces, even on a superfine capillary with the bending radius down to 0.15 mm. After the devices complete their functions, they can rapidly degrade in ambient water without any toxic byproducts, effectively reducing environmental pollution. More strikingly, proton conduction is confirmed to exist in neutral polysaccharides, and the protons originate from the self‐dissociation of water, which provides a meaningful guideline for future synaptic transistors based on neutral natural biomaterials.

Ultrathin organic thin-film transistors (OTFTs) have received extensive attention due to their outstanding advantages, such as extreme flexibility, good conformability, ultralight weight, and compatibility with low-cost and large-area solution-processed techniques. However, compared with the rigid substrates, it still remains a challenge to fabricate high-performance ultrathin OTFTs. In this study, a high-performance ultrathin 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) OTFT array is demonstrated via a simple spin-coating method, with mobility as high as 11 cm V s (average mobility: 7.22 cm V s ), on/off current ratio of over 10 , switching current of >1 mA, and a good yield ratio as high as 100%. The ultrathin thickness at ≈380 nm and the ultralight weight at ≈0.89 g m enable the free-standing OTFTs to imperceptibly adhere onto human skin, and even a damselfly wing without affecting its flying. More importantly, the OTFTs show good electrical characteristics and mechanical stability when conformed onto the curved surfaces and even folded in a book after 100 folding cycles. These results illustrate the broad application potential of this simply fabricated ultrathin OTFT in next-generation electronics such as foldable displays and wearable devices.

Well-faceted hexagonal ZnO nanotubes were synthesized by a simple hydrothermal method and the subsequent aging process without any catalysts or templates. The formation of the tubular structure is closely linked to the polarity of ZnO and the selective adsorption behavior of Zn2+ amino complexes. The surface-related optical properties were studied with use of Raman and photoluminescence spectra. It was found that the oxygen vacancy-related visible emission intensity decreased while surface defect-related visible emission intensity increased when the nanotubes were annealed in oxygen ambient. The anomalous enhancement of PL integrated intensity with the temperature shows fairly high surface state density existing in ZnO nanotubes.

features beyond mechanical flexibility such as wearability, stretchability, portability, and biocompatibility. For instance, Chen's group successfully demonstrated stretchable motion memory devices based on mechanical hybrid materials, which can work in the wearable state. [25] In order to achieve those properties, the nonconventional substrates are usually necessary to integrate with the devices, such as flexible organics, biocompatible polymer, and nonplanar substrates. However, these substrates may possess poor tolerance for high temperature during the device fabrication. In general, there exist two approaches to obtain functional devices on the arbitrary nonconventional substrates. On the one hand, as the reviewer mentioned, the flexible organic devices can be directly fabricated on these desired substrates due to the low-temperature processing of organic materials. [26][27][28][29] On the other hand, fabrication of transferable or free-standing devices is a more universal method for the integration with nonconventional substrates, which is applicable not only to organic materials but also to inorganic materials. [30][31][32][33] As a matter of fact, fabrication of inorganic devices on nonconventional substrates is usually faced with some difficulties. For example, the thermal processing, which is necessary in some cases to obtain high-quality films, may limit the use of organic and biocompatible polymer substrates; the shadow effect of physical deposition (e.g., sputtering or pulsed laser deposition), which is usually employed to deposit inorganic films, can result in the film nonuniformity when they are fabricated on nonplanar substrates. Thus, the development of transferable and free-standing electronic devices can well protect the functional substrates from harsh processing, and also, the transferable devices can be stuck conformally onto the desired substrates (like 3D-curve or folded) to realize future applications on wearable computers, epidermal electronics, and implantable chips. For example, Wan et al. have successfully demonstrated free-standing artificial synapses using 3D protoncoupled transistors on chitosan membranes. [33] Recently, two-terminal memristors have been proposed as one promising candidate for the artificial synapses thanks to its variable conductance in analogy with the change of synapse weight. [34][35][36][37][38] A variety of materials, such as metal oxides, [34][35][36] chalcogenide, [37] Si, [38] Perovskite, [39,40] and organics, [41] have been employed as building blocks of memristor-based artificial synapses. Diverse synaptic functions atThe absence of an effective approach to achieve free-standing inorganic memristors seriously hinders the development of transferable artificial synapses. Here, a transferable WO x -based memristive synapse is demonstrated using a nondestructive water-dissolution method in which the NaCl substrate is selected as the sacrificial layer due to its thermotolerance and water-solubility. The essential synaptic learning functions are achieved to com...