a as the spacer, without the use of any stand-alone spacer. The bE harge-discharge cycles of the battery were measured between 3.6 and 0.1 V, at a constant current of 10 mA/g. A large irreversible-capacity(430 mAh/g) is observed during the first harge-discharge cycle(Fig 3a), and further charge-discharge Discharge cycles resulted in a reversible capacity of 110 mAh/g(Fig. 3b; see SI). The battery device operates under full mechanical flexibil- :::::,, ity. The laminated Li-ion-based battery device was used to lig up a red light-emitting diode(Fig. 3c), showing its discharge /g) Number of cycles behavior. The demonstration could be repeated over several tens of cycles of charging and discharging C In recent years, supercapacitors coupled with batteries have been considered as promising hybrid devices(25, 26)to combine the best features of a battery and a supercapacitor. We show that our battery and supercapacitor devices could be integrated in arallel to build hybrids, as reported for conventional hybrids ig. 4a). In this case, the battery segment of the hybrid is used harge the adjoining supercapacitor. In addition to this Fig3. Electrochemical measurements of nanocomposite paper battery. (a) traditional hybrid, the nanocomposite units also allow for build irst charge-discharge curves of the nanocomposite thin-film battery cycled ing new kinds of merged hybrid devices(27)(with three termi- tween 3.6 and o 1 V at a constant current of 10 mA/g.(b)Charge capacity nals; Fig. 4b, see legend for the definition of the terminals), nanocomposite film battery used to glow ared light-emitting diode (LED). The storage device). The Li metal layer(anode; terminal 2)and in film present on one side as one of the electrodes. The lEd glows ey when thebattery device is rolled up, and the demonstration could berepeated of aqueous electrolyte(1 LiPF6) forms the battery part of over several tens of cycles at an initial operating voltage of 2.1 V anocomposite unit MWNT terminal )-cellulose-RTIL assembled adjacent to the battery on the The fabrication of the flexible Li-ion battery based on the 1 and 3. During the operation of the device, the Li electrode nanocomposite paper consists of RTIL-free nanocomposite as (terminal 2)and the supercapacitor electrode(terminal 1)are cathode and a thin evaporated Li-metal layer as anode(Fig. 1 shorted, and the discharge of the battery is used to charge the with Al foil on both sides as current collectors. Aqueous 1 M supercapacitor. The charging of the supercapacitor takes place LiPF6 in ethylene carbonate and dimethyl carbonate (1: 1 vol/vol) because of intercalation at terminal 2; a PF-6 double layer forn is used as the electrolyte. As with the supercapacitor, the battery on the surface of the battery cathode(terminal 3), in addition also uses the excess cellulose layer in the nanocomposite cathode the electric double layer formed at the supercapacitor electrode a Li electrode current collectors b 2.0 d 4 1.5 discharge of battery discharge of battery 0150300450 0306090120 itor-battery hybrid energy devices based on nanocomp ercapacitor and battery in parallel configuration. (b)The di discha its(a) Schematic of a four-terminal hybrid-energy device showing the Dacito ge curve of battery and supercapacitor is plotted as a function oftime.The charges the supercapacitor, and subsequently the supercapacitor is discharged. () Schematic of a three-terminal hybrid energy device that can act as both supercapacitor and battery. The three terminals are defined, and the battery and supercapacitor segments of the device are shown. (d) The discharge behavior of the battery and subsequent discharge of supercapacitor are shown. The battery is discharged with terminals 1 and 2 shorted. This simultaneously charges the supercapacitor following the double layer formation at the electrode interface. Subsequently, the supercapacitor is discharged across erminals 1 and 3. An additional separator(glass fibers)is normally added along with the excess cellulose spacer to improve behavior 13576iwww.pnas.org/cgi/doi/10.1073/pnas.0706508104 Pushparaj et al.The fabrication of the flexible Li-ion battery based on the nanocomposite paper consists of RTIL-free nanocomposite as cathode and a thin evaporated Li-metal layer as anode (Fig. 1a), with Al foil on both sides as current collectors. Aqueous 1 M LiPF6 in ethylene carbonate and dimethyl carbonate (1:1 vol/vol) is used as the electrolyte. As with the supercapacitor, the battery also uses the excess cellulose layer in the nanocomposite cathode as the spacer, without the use of any stand-alone spacer. The charge–discharge cycles of the battery were measured between 3.6 and 0.1 V, at a constant current of 10 mA/g. A large irreversible-capacity (430 mAh/g) is observed during the first charge–discharge cycle (Fig. 3a), and further charge–discharge cycles resulted in a reversible capacity of 110 mAh/g (Fig. 3b; see SI). The battery device operates under full mechanical flexibil￾ity. The laminated Li-ion-based battery device was used to light up a red light-emitting diode (Fig. 3c), showing its discharge behavior. The demonstration could be repeated over several tens of cycles of charging and discharging. In recent years, supercapacitors coupled with batteries have been considered as promising hybrid devices (25, 26) to combine the best features of a battery and a supercapacitor. We show that our battery and supercapacitor devices could be integrated in parallel to build hybrids, as reported for conventional hybrids (Fig. 4a). In this case, the battery segment of the hybrid is used to charge the adjoining supercapacitor. In addition to this traditional hybrid, the nanocomposite units also allow for build￾ing new kinds of merged hybrid devices (27) (with three termi￾nals; Fig. 4b, see legend for the definition of the terminals), which would act as both battery and supercapacitor (a dual￾storage device). The Li metal layer (anode; terminal 2) and RTIL-free nanocomposite film (cathode; terminal 3) with a drop of aqueous electrolyte (1 M LiPF6) forms the battery part of the hybrid, whereas the nanocomposite unit [MWNT (terminal 1)–cellulose–RTIL] assembled adjacent to the battery on the side of the Li layer forms the supercapacitor between terminals 1 and 3. During the operation of the device, the Li electrode (terminal 2) and the supercapacitor electrode (terminal 1) are shorted, and the discharge of the battery is used to charge the supercapacitor. The charging of the supercapacitor takes place because of intercalation at terminal 2; a PF6 double layer forms on the surface of the battery cathode (terminal 3), in addition to the electric double layer formed at the supercapacitor electrode Fig. 3. Electrochemical measurements of nanocomposite paper battery. (a) First charge–discharge curves of the nanocomposite thin-film battery cycled between 3.6 and 0.1 V at a constant current of 10 mA/g. (b) Charge capacity vs. number of cycles of the nanocomposite thin-film battery. (c) The flexible nanocomposite film battery used to glow a red light-emitting diode (LED). The flexible battery consists of an individual nanocomposite thin film with the Li thin film present on one side as one of the electrodes. The LED glows even when the battery device is rolled up, and the demonstration could be repeated over several tens of cycles at an initial operating voltage of 2.1 V. Fig. 4. Supercapacitor-battery hybrid energy devices based on nanocomposite units. (a) Schematic of a four-terminal hybrid-energy device showing the arrangement of supercapacitor and battery in parallel configuration. (b) The discharge curve of battery and supercapacitor is plotted as a function of time. The discharge of battery charges the supercapacitor, and subsequently the supercapacitor is discharged. (c) Schematic of a three-terminal hybrid energy device that can act as both supercapacitor and battery. The three terminals are defined, and the battery and supercapacitor segments of the device are shown. (d) The discharge behavior of the battery and subsequent discharge of supercapacitor are shown. The battery is discharged with terminals 1 and 2 shorted. This simultaneously charges the supercapacitor following the double-layer formation at the electrode interface. Subsequently, the supercapacitor is discharged across terminals 1 and 3. An additional separator (glass fibers) is normally added along with the excess cellulose spacer to improve behavior. 13576
www.pnas.orgcgidoi10.1073pnas.0706508104 Pushparaj et al.