Electronic skin (e-skin) presents a network of mechanically flexible sensors that can conformally wrap irregular surfaces and spatially map and quantify various stimuli 1-12 . Previous works on e-skin have focused on the optimization of pressure sensors interfaced with an electronic readout, whereas user interfaces based on a human-readable output were not explored. Here, we report the first user-interactive e-skin that not only spatially maps the applied pressure but also provides an instantaneous visual response through a built-in active-matrix organic light-emitting diode display with red, green and blue pixels. In this system, organic light-emitting diodes (OLEDs) are turned on locally where the surface is touched, and the intensity of the emitted light quantifies the magnitude of the applied pressure. This work represents a system-on-plastic 4,13-17 demonstration where three distinct electronic componentsthin-film transistor, pressure sensor and OLED arrays-are monolithically integrated over large areas on a single plastic substrate. The reported e-skin may find a wide range of applications in interactive input/control devices, smart wallpapers, robotics and medical/health monitoring devices.Although both passive 6,8,12 and active-matrix 1,2,5,9 designs can be used for enabling the predicted user-interactive e-skins, the active-matrix design is advantageous as it minimizes signal crosstalk and thereby offers better spatial resolution and contrast, and a faster response. In the active-matrix backplane circuitry, each pixel is controlled by a thin-film transistor (TFT) that acts as a switch for addressing either current-or voltage-driven devices. Here, we incorporate the active-matrix design into the e-skin by using semiconductor-enriched nanotubes 18 as the channel material of the TFTs. Carbon nanotube networks are proven to be a promising material platform for high-performance TFTs (refs 9,17,19-21) with high current drives needed for switching OLEDs (ref. 22). A schematic structure of a pixel of the user-interactive e-skin with an integrated TFT, OLED and pressure sensor is depicted in Fig. 1a. Each pixel in the active-matrix consists of a nanotube TFT with the drain connected to the anode of an OLED. The OLED uses a simple bilayer structure 23 and the colour of the emitted light is controlled by using different emissive layer materials (details in the Methods). In this work, red, green, blue and yellow colours are demonstrated. On top of the OLEDs, a pressure-sensitive rubber 1,5,24,25 (PSR) is laminated, which is in electrical contact with the cathode (that is, top contact) of the OLED at each pixel. The top surface of the PSR is coated with a conductive silver ink to act as the ground contact. Here, the conductivity of the PSR increases by an applied pressure 1,5,24,25 in the underlying OLED turning on. As illustrated in Fig. 1b, the single-pixel circuitry is integrated into an active-matrix array. The resulting system-on-plastic provides a touch user interface, allowing the pressure profile to be...

Innovation in the design of electrolyte materials is crucial for realizing next-generation electrochemical energy storage devices such as Li–S batteries. The theoretical capacity of the S cathode is 10 times higher than that of conventional cathode materials used in current Li–ion batteries. However, Li–S batteries suffer from the dissolution of lithium polysulfides, which are formed by the redox reaction at the S cathode. Herein, we present simple solvate ionic liquids, glyme–Li salt molten complexes, as excellent electrolyte candidates because they greatly suppress the dissolution of lithium polysulfides. The molten complexes do not readily dissolve other ionic solutes, which leads to the stable operation of the Li–S battery over more than 400 cycles with discharge capacities higher than 700 mAh g-sulfur−1 and with coulombic efficiencies higher than 98% throughout the cycles. Such high performance has not been realized to the best of our knowledge. Furthermore, the addition of a nonflammable fluorinated solvent, which does not break the solvate structure of the glyme–Li salt molten complexes, greatly enhances the power density of the Li–S battery. The strategic design of electrolyte properties provides opportunities for the development of new electrochemical devices with many different electrode materials.

A variety of binary mixtures of aprotic ionic liquids (ILs) and lithium salts were thoroughly studied as electrolytes for rechargeable lithium-sulfur (Li-S) batteries. The saturation solubility of sulfur and lithium polysulfides (Li 2 S m ), the active materials in the Li-S battery, in the electrolytes was quantitatively determined, and the performance of the Li-S battery using the electrolytes was also investigated. Although the solubility of nonionic sulfur was low in all of the electrolytes evaluated, the solubility of Li 2 S m in the IL-based electrolyte was strongly dependent on the anionic structure, and the difference in the solubility could be rationalized in terms of the donor ability of the IL solvent.Dissolution of Li 2 S m in the ILs with strong donor ability was comparable to that achieved with typical organic electrolytes; the strongly donating IL electrolyte did not prevent redox shuttle reaction in the Li-S cells. The battery performance was also influenced by unfavorable side reactions of the anions (such as tetrafluoroborate (BF 4 − ) and bis(fluorosulfonylamide) ([FSA] − )) with polysulfides and by slow mass transport in viscous ILs, even though the dissolution of Li 2 S m into the IL electrolyte was greatly suppressed. Among the IL-based electrolytes, the low-viscosity [TFSA]-based ILs facilitated stable charge/discharge of the Li-S batteries with high capacity and high coulombic efficiency. The unique solvent effect of the ILs can thus be exploited in the Li-S battery by judicious selection of ILs that exhibit high lithium-ion-transport ability and electrochemical stability in the presence of Li 2 S m .

A room temperature ionic liquid (RTIL), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)amide ([DEME][TFSA]), was used as an electrolyte solvent for lithium–sulfur (Li–S) batteries. Li[TFSA] was dissolved into [DEME][TFSA] to prepare the electrolytes, and a molecular solventtetraethylene glycol dimethyl ether (TEGDME)was used for Li[TFSA] as a reference. Discharge–charge tests of Li–S cells using these electrolytes were carried out. The discharge–charge cycle stability and Coulombic efficiency of a cell with an RTIL electrolyte were found to be surprisingly superior to those of a cell with TEGDME electrolyte. The poor cycle stability of the cell with the TEGDME electrolyte was attributed to the dissolution of lithium polysulfides (Li2S m ), which were generated as reaction intermediates through a redox process at the S cathode in the Li–S cell. RTIL has low donor ability owing to the weak Lewis basicity of [TFSA]− anion, whereas conventional ether-based molecular solvents such as TEGDME have high donor ability. The dissolution of Li2S m was significantly suppressed owing to the weak donor ability of RTIL. In the RTIL electrolyte, Li2S m was immobilized on the electrode, and the electrochemical reaction of the S species occurred exclusively in the solid phase. These results clearly prove a novel solvent effect of RTILs on the electrochemical reactions of the S cathode in Li–S cells.

A series of equimolar mixtures of Li salts (LiX) and glymes (triglyme (G3) and tetraglyme (G4)), [Li(glyme)]X with different anions (X: [N(SO2C2F5)2] = [BETI]; [N(SO2CF3)2] = [TFSA]; [CF3SO3] = [OTf]; BF4; NO3), were used as electrolytes to study the anionic effects of [Li(glyme)]X on the performance of lithium–sulfur (Li–S) batteries. The dissolution of lithium polysulfides (Li2S m ), which are discharge products of elemental sulfur, was significantly suppressed in the solvate ionic liquid (IL) electrolytes, as seen in [Li(G4)][BETI] and [Li(glyme)][TFSA], wherein all of the glymes participated in the formation of the complex cation [Li(glyme)]+. It was found that NO3 anions were irreversibly reduced at the composite cathode during discharge and BF4 anions formed unexpected byproducts through a chemical reaction with the polysulfide anions. Successful charge/discharge of Li–S cell could not be performed in [Li(glyme)]X in the presence of these anions because of the undesired side reactions. The solvate IL [Li(G4)][BETI] was found to be electrochemically stable in the Li–S cell and allowed a stable operation with a capacity of 600–700 mAh·g–1 and a Coulombic efficiency of 98.5% over 100 cycles, similar to that achieved by [Li(glyme)][TFSA]. In contrast, the Li–S cell with a concentrated electrolyte solution, [Li(G3)][OTf], showed a much lower capacity and Coulombic efficiency.