Flexible lithium-ion batteries are necessary for powering the next generation of wearable electronic devices. In most designs, the mechanical flexibility of the battery is improved by reducing the ...thickness of the active layers, which in turn reduces the areal capacity and energy density of the battery. The performance of a battery depends on the electrode composition, and in most flexible batteries, standard electrode formulation is used, which is not suitable for flexing. Even with considerable efforts made toward the development of flexible lithium-ion batteries, the formulation of the electrodes has received very little attention. In this study, we investigate the relation between the electrode formulation and the mechanical strength of the electrodes. Peel and drag tests are used to compare the adhesion and cohesion strength of the electrodes. The strength of an electrode is sensitive to the particle size and the choice of polymeric binder. By optimizing the electrode composition, we were able to fabricate a high areal capacity (∼2 mAh/cm2) flexible lithium-ion battery with conventional metal-based current collectors that shows superior electrochemical and mechanical performance in comparison to that of batteries with standard composition.
This paper reports on the design and operation of a flexible power source integrating a lithium ion battery and amorphous silicon solar module, optimized to supply power to a wearable health ...monitoring device. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide, respectively, on thin flexible current collectors. It displays energy density of 6.98 mWh/cm(2) and demonstrates capacity retention of 90% at 3C discharge rate and ~99% under 100 charge/discharge cycles and 600 cycles of mechanical flexing. A solar module with appropriate voltage and dimensions is used to charge the battery under both full sun and indoor illumination conditions, and the addition of the solar module is shown to extend the battery lifetime between charging cycles while powering a load. Furthermore, we show that by selecting the appropriate load duty cycle, the average load current can be matched to the solar module current and the battery can be maintained at a constant state of charge. Finally, the battery is used to power a pulse oximeter, demonstrating its effectiveness as a power source for wearable medical devices.
A stretchable alkaline battery based on a embedded stretchable silver fabric is fabricated with an open circuit potential (OCV) of 1.5 V and capacity of 3.775 mAh/cm2. No drop in discharge capacity ...is observed with strain up to 100%. Two batteries connected in series continued to power a red LED even when stretched to 150% and twisted by 90 degrees.
Highly flexible, printed alkaline batteries based on a mesh‐embedded architecture are demonstrated. The mesh acts as a support for the electroactive material during flexing. Two cells connected in ...series and bent to a radius of 0.3 cm are used to power a green light‐emitting diode (LED).
Additive and low-temperature printing processes enable the integration of diverse electronic devices, both power-supplying and power-consuming, on flexible substrates at low cost. Production of a ...complete electronic system from these devices, however, often requires power electronics to convert between the various operating voltages of the devices. Passive components-inductors, capacitors, and resistors-perform functions such as filtering, short-term energy storage, and voltage measurement, which are vital in power electronics and many other applications. In this paper, we present screen-printed inductors, capacitors, resistors and an RLC circuit on flexible plastic substrates, and report on the design process for minimization of inductor series resistance that enables their use in power electronics. Printed inductors and resistors are then incorporated into a step-up voltage regulator circuit. Organic light-emitting diodes and a flexible lithium ion battery are fabricated and the voltage regulator is used to power the diodes from the battery, demonstrating the potential of printed passive components to replace conventional surface-mount components in a DC-DC converter application.
Early demonstrations of wearable devices have driven interest in flexible lithium‐ion batteries. Previous demonstrations of flexible lithium‐ion batteries trade off between low areal capacity, poor ...mechanical flexibility and/or high thickness of inactive components. Here, a reinforced electrode design is used to support the active layers of the battery and a freestanding carbon nanotube (CNT) layer is used as the current collector. The supported architecture helps to increase the areal capacity (mAh cm‐2) of the battery and improve the tensile strength and mechanical flexibility of the electrodes. Batteries based on lithium cobalt oxide and lithium titanate oxide shows excellent electrochemical and mechanical performance. The battery has an areal capacity of ≈1 mAh cm‐2 and a capacity retention of around 94% after cycling the battery for 450 cycles at a C/2 rate. The reinforced electrode has a tensile strength of ≈5.5–7.0 MPa and shows excellent capacity retention after repeatedly flexing to a bending radius ranging from 45 to 10 mm. The relationships between mechanical flexing, electrochemical performance, and mechanical integrity of the battery are studied using electrochemical cycling, electron microscopy, and electrochemical impedance spectroscopy (EIS).
Flexible lithium‐ion batteries with a high areal capacity of ≈1 mAh cm‐2 and an open‐circuit potential of 2.6 V are demonstrated. Due to the reinforced electrode design, the batteries are able to maintain their capacity, even after repeated flexing up to a bend radius of 10 mm.
Traditional printing methods offer the advantage of well‐matured technology, high accuracy of depositing inks over flexible substrates at high web speeds, and low cost of fabrication. The components ...of a battery—the current collectors, active layers, and separator—can all be deposited using conventional printing techniques by designing suitable inks. A combination of low thickness of printed electrodes, flexible packaging, battery architecture, and material properties makes printed batteries flexible. In this paper, we will discuss material challenges and mechanical limits of flexible printed batteries. We will review several printing techniques and present examples of batteries printed using these methods. In addition, we will briefly discuss other novel non‐printed compliant batteries that have unique mechanical form.
Printed flexible batteries: Compliant power sources are necessary for powering the next generation of flexible and wearable electronic devices. In this Review, the material challenges and mechanical limits of flexible printed batteries are discussed. The authors review several printing techniques, and present examples of batteries printed using these methods, in addition to introducing other novel non‐printed compliant batteries that have unique mechanical form.
Identification of solvents for dissolving polymer dielectrics and organic semiconductors is necessary for the fabrication of solution-processed organic field effect transistors (OFETs). In addition ...to solubility and printability of a solvent, orthogonality is particularly important when forming multilayer structure from solutions. Currently, the process of finding orthogonal solvents is empirical, and based on trial-and-error experimental methods. In this paper, we present a methodology for identifying orthogonal solvents for solution-processed organic devices. We study the accuracy of Hildebrand and Hansen solubility theories for building solubility boundaries for organic semiconductor (Poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno3,2-bthiophene (PBTTT) and polymer dielectrics (Poly(methyl methacrylate) (PMMA), Polystyrene (PS)). The Hansen solubility sphere for the organic semiconductor and polymer gate dielectrics are analyzed to identify solvents that dissolve PMMA and PS, but are orthogonal to PBTTT. Top gate/bottom contact PBTTT based OFETs are fabricated with PMMA gate dielectric processed with solvents that are orthogonal and non-orthogonal to PBTTT. The non-orthogonal solvents swell the semiconductor layer and increase their surface roughness.
A methodology for identifying orthogonal solvents for solution-processed organic field effect transistor is reported. Hildebrand and Hansen solubility theory is used to construct solubility boundary for commonly used organic semiconductors and polymer gate dielectrics. The effect of orthogonality of a polymer dielectric solution on the semiconductor morphology and electrical characteristics of OFETs is studied. Display omitted
•A methodology to identify orthogonal solvents for solution-processed devices is presented.•Solvents orthogonal to PBTTT are identified.•The effect of orthogonality of polymer dielectric solution on the mobility and morphology of PBTTT is studied.
Compliant energy storage has not kept pace with flexible electronics. Herein we demonstrate a technique to reinforce arbitrary battery electrodes by supporting them with mechanically 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–MnO2 battery with printed current collectors. The Zn and MnO2 electrodes were prepared by using a solution‐based embedding process. The cell had a nominal potential of 1.5 V and an effective capacity 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 MnO2 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.
Bend and flex: A high‐energy‐density, nontoxic Zn–MnO2 battery with printed current collectors is fabricated. The Zn and MnO2 electrodes are prepared by using a solution‐based embedding process. The cell has a nominal potential of 1.5 V and an effective capacity of approximately 3 mA h cm−2. The effects of bending and fatigue on the electrochemical performance and mechanical integrity of the battery are investigated.
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