DOI: 10.1002/ente.201200027 Reinforced Electrode Architecture for a Flexible Battery with Paperlike Characteristics Abhinav M. Gaikwad, [a] Howie N. Chu, [a] Rigers Qeraj, [a] Alla M. Zamarayeva, [a] and Daniel A. Steingart* [a, b] Introduction Low-cost, disposable, flexible batteries, fabricated by using high-throughput manufacturing techniques, are a prerequisite for many proposed conformal medical [1] and sensing devi- ces. [2] Recently, there have been many demonstrations of compliant electrochemical- and capacitive-based power sour- ces such as printed flexible batteries, [3–13] supercapacitors, [14–16] and stretchable batteries. [17, 18] Currently, commercially avail- able flexible batteries have mechanical limitations and a rela- tively low areal capacity. Moreover, the discharge perfor- mance decreases after repeated flexing. [11] Even with ad- vancements in the fabrication of strain-compliant silicon- based flexible/stretchable electronic devices by leveraging new architectures, there has been insufficient effort towards the improvement of the mechanical characteristics of flexible batteries. [11, 17] We have previously examined an elastic elec- trode structure. [18] In this work, we fabricate flexible batteries by using a fibrous membrane template [19] and subsequently examine the relationship between the mechanical state and lifetime. Flexible electronics such as displays, [20] photovoltaic cells, [21] organic light-emitting diodes (OLEDs), [22] radio-fre- quency identification (RFID) tags, [23] pressure sensors, [24] and thin-film-transistor (TFT) backplanes [25] have been demon- strated. The materials used in these devices are inherently hard and brittle in bulk form but can be made flexible by de- positing or patterning them in thin forms. [26–29] Brittle materi- als can typically be made flexible by reducing their thickness to 1/1000th of the bending radius. [30] One can use a similar concept to make flexible batteries. [31] However, batteries are closed electrochemical reactors, and the capacity of the bat- tery is dependent on the mass of the reactants (anode/cath- ode) enclosed within. Thus, traditional thin-film batteries have insufficient capacity per area for most applications. [32, 33] One issue with designs dependent on reduced thickness is the unnecessary coupling of the mechanical and electrochem- ical performance. In this work, we use a composite architec- ture in which we combine a porous membrane with a battery electrode to improve its flexing characteristics. We used a nonwoven polyimide (PI) membrane with a high tensile strength as a scaffold for the two electrodes, which were then fabricated into a flexible Zn–MnO 2 battery. The flexible elec- trodes were prepared by embedding the anode and cathode inside the PI membrane. The membrane supports the elec- trode mix and absorbs the stress generated during flexing. Printed C and Ag electrodes were used as the anodic and cathodic current collectors, respectively. The anode and cath- ode were sealed within two sheets of flexible polyvinylchlor- ide (PVC). The capacity of the battery was cathode-limited by design. In this work, we discuss the modes of failure in a thin-film flexible battery and study the effect of the sign of Compliant energy storage has not kept pace with flexible electronics. Herein we demonstrate a technique to reinforce arbitrary battery electrodes by supporting them with me- chanically tough, low-cost fibrous membranes, which also serve as the separator. The membranes were laminated to form a full cell, and this stacked membrane reinforcement bears the loads during flexing. This technique was used to make a high energy density, nontoxic Zn–MnO 2 battery with printed current collectors. The Zn and MnO 2 electrodes were prepared by using a solution-based embedding process. The cell had a nominal potential of 1.5 V and an effective capaci- ty of approximately 3 mA h cm 2 . We investigated the effect of bending and fatigue on the electrochemical performance and mechanical integrity of the battery. The battery was able to maintain its capacity even after 1000 flex cycles to a bend radius of 2.54 cm. The battery showed an improvement in discharge capacity (ca. 10 %) if the MnO 2 electrode was flexed to tension as a result of the improvement of particle- to-particle contact. In a demonstration, the flexible battery was used to power a light-emitting diode display integrated with a strain sensor and microcontroller. [a] A. M. Gaikwad, + H. N. Chu, + R. Qeraj, A. M. Zamarayeva, Prof. D. A. Steingart Energy Institute, Chemical Engineering Department City College of New York 160 Convent Ave., New York, NY 10031 (USA) [b] Prof. D. A. Steingart Current Address: Department of Mechanical and Aerospace Engineering Princeton University D428 Engineering Quadrangle Princeton, NJ 08544 (USA) E-mail: steingart@princeton.edu [ + ] These authors contributed equally to this work. Energy Technol. 0000, 00, 1 – 10  2013 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim &1& These are not the final page numbers! ÞÞ