30-07-2012, 04:32 PM
Thin, Flexible Secondary Li-Ion Paper Batteries
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ABSTRACT
There is a strong interest in thin, flexible energy storage devices to meet modern society needs
for applications such as interactive packaging, radio frequency sensing, and consumer products. In this article, we
report a new structure of thin, flexible Li-ion batteries using paper as separators and free-standing carbon
nanotube thin films as both current collectors. The current collectors and Li-ion battery materials are integrated
onto a single sheet of paper through a lamination process. The paper functions as both a mechanical substrate and
separator membrane with lower impedance than commercial separators. The CNT film functions as a current
collector for both the anode and the cathode with a low sheet resistance (5 Ohm/sq), lightweight (0.2 mg/
cm2), and excellent flexibility. After packaging, the rechargeable Li-ion paper battery, despite being thin
(300 m), exhibits robust mechanical flexibility (capable of bending down to<6 mm) and a high energy
density (108 mWh/g).
There is a great need for development of lightweight,
thin, and flexible batteries for portable electronic
applications with low power consumption, 1.0
mW. Ajayan et al. developed flexible batteries and supercapacitors
based on nanocomposite paper in 2007;
Mihranyan et al. developed ultrafast all-polymer paperbased
batteries in 2009; and we explored conductive
paper for energy storage recently.7,21,22 Enfucell Inc. and
Blue Spark Inc. have recently developed a flexible and
soft battery by using a printing method on plastic substrates.
The Li-ion paper battery developed in this article
has advantages in various aspects. In Ajayan’s
nanocomposite-based battery, Li metal was used as
one electrode and is neither thin nor flexible. The polymer
battery developed by Mihranyan et al. performs as
a mixed battery and capacitor, which shows a nonflat
discharge curve and has a large thickness (2 mm). The
soft batteries from Enfucell and Blue Spark are made
on plastic substrates, not paper, and are not rechargeable.
Figure 4e and Table 1 in Supporting Information
show the comparison of our flexible, thin paper battery
with theirs. The blue arrow indicates the improvement
direction for flexible storage devices.