Thin, Flexible Secondary Li-Ion Paper Batteries

Abstract

These authors contributed equally to this work. Integration of electronics onto existing, widely used paper could bring unprecedented opportunities for consumer electronics.1Ϫ3 These devices can be paperthin, flexible, lightweight and manufactured by a low cost, roll-to-roll printing process. Power sources are needed for the operation of the paper electronics, and ideally, a power source directly integrated onto paper would be preferred for easy system integrations. On the other hand, secondary Li-ion batteries are key components in portable electronics due to their high power and energy density and long cycle life. 4 In these devices, metal strips, mainly copper (ϳ10 mg/cm 2 ) and aluminum (5 mg/cm 2 ), are used as current collectors. Recently, solution-processed carbon nanotube (CNT) thin films have been widely studied and applied as electrodes for optoelectronics due to their high conductivity and flexibility. 3,5 CNT thin films on plastic substrates have been explored as current collectors for supercapacitors. 6 We recently demonstrated that paper coated with CNTs or silver nanowires can be used to replace heavy metals in supercapacitors and Li-ion batteries. 7 The CNT films on substrate function effectively as current collectors and enable some new properties for devices.In this paper, we integrated all of the components of a Li-ion battery into a single sheet of paper with a simple lamination process. Free-standing, lightweight CNT thin films (ϳ0.2 mg/cm 2 ) were used as current collectors for both the anode and cathode and were integrated with battery electrode materials through a simple coating and peeling process. The double layer films were laminated onto commercial paper, and the paper functions as both the mechanical support and Li-ion battery membrane. Due to the intrinsic porous structure of the paper, it functions effectively as both a separator with lower impedance than commercial separators and has good cyclability (no degradation of Li-ion battery after 300 cycles of recharging). After polymer sealing, the secondary Li-ion battery is thin (Ͻ300 m), mechanically flexible, and has a high energy density. Such flexible secondary batteries will meet many application needs in applications such as interactive packaging, radio frequency sensing, and electronic paper.CNT thin films were coated onto stainless steel (SS) substrates with a solutionbased process. Aqueous CNT ink was prepared with 10% by weight sodium dodecylbenzenesulfonate (SDBS) as the surfactant. 8 The concentration of CNT is 1.7 mg/mL. The CNT ink was applied to the SS substrate with a doctor blade method.

Paper‐Based Electrodes for Flexible Energy Storage Devices

“…15 The LTO/CNT and LCO/CNT films were then easily delaminated from the substrates by simply immersing them into DI water and peeling off. After that, the LTO/CNT and LCO/CNT films were rolled to the paper via coating a thin layer of PVDF in between, which the PVDF functions as a glue to stick the double layer films on paper.…”

“…Such a “rate‐limiting step” has greatly impeded the commercialization of these electronics. In order to overcome this limiting factor, extensive efforts have been devoted to make flexible and high performance energy storage devices 12, 13, 14, 15, 16, 17, 18, 19…”

Stretchable batteries with self-similar serpentine interconnects and integrated wireless recharging systems

“…For many of these and other uses, a critical need lies in energy-storage devices with similar physical properties, to allow for direct and natural integration with the electronics 14 . Many important storage devices have been developed with flexible characteristics, including supercapacitors [15][16][17] and batteries 17,18 , where sufficiently thin geometrical forms lead to flexibility, by virtue of bending-induced strains (typically to values of B1% or less) that decrease linearly with thickness, for a given bend radius. Stretchability, on the other hand, represents a more challenging type of mechanics, in which the systems must accommodate large strain deformation (c1%), typically of arbitrary form, including not only bending, but also twisting, stretching, compressing and others, and thickness is typically not a critical factor.…”

Fiber‐Type Solar Cells, Nanogenerators, Batteries, and Supercapacitors for Wearable Applications

“…Among all energy storage devices, LIB has revolutionized the modern consumer electronics industry owing to its high energy density, light‐weight, good cyclic stability, and environmentally friendly operation. Recently, many researchers are working toward the development of thin and flexible LIBs 106, 107, 108. In developing wearable devices, a fiber‐shaped LIB offers considerable advantages over a planar structure, since it can be easily bent, twisted, stretched, and woven into porous textiles that allow air permeation.…”