31-10-2012, 03:41 PM
Thin, Flexible Secondary Li-Ion Paper Batteries
[attachment=37599]
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).
INTRODUCTION
Integration of electronics onto existing,
widely used paper could bring unprecedented
opportunities for consumer
electronics.13 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
(10 mg/cm2) and aluminum (5 mg/cm2),
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.
Fabrication and Test of Li-Ion Batteries:
For half cell tests of LTO/
CNT and LCO/CNT, coin cells were fabricated. Lithium metal foil
(Alfa Aesar) was used as the counter electrode in each case.
Xerox paper was used as the separator. Lithium metal and freestanding
LTO/CNT or LCO/CNT films were punched into round
shapes. The parts for coin cell assembly were purchased from
MTI Corporation (Richmond, CA). A 1 M solution of LiPF6 in EC/
DEC (1:1 vol/vol; Ferro) was used as the electrolyte. The charge/
discharge cycles were performed at different rates at room temperature.
The devices were assembled in an argon-filled
glovebox with oxygen and water contents below 1 and 0.1 ppm,
respectively. The Li-ion battery tests were performed by either a
Bio-Logic VMP3 battery tester or an MTI battery analyzer.
[attachment=37599]
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).
INTRODUCTION
Integration of electronics onto existing,
widely used paper could bring unprecedented
opportunities for consumer
electronics.13 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
(10 mg/cm2) and aluminum (5 mg/cm2),
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.
Fabrication and Test of Li-Ion Batteries:
For half cell tests of LTO/
CNT and LCO/CNT, coin cells were fabricated. Lithium metal foil
(Alfa Aesar) was used as the counter electrode in each case.
Xerox paper was used as the separator. Lithium metal and freestanding
LTO/CNT or LCO/CNT films were punched into round
shapes. The parts for coin cell assembly were purchased from
MTI Corporation (Richmond, CA). A 1 M solution of LiPF6 in EC/
DEC (1:1 vol/vol; Ferro) was used as the electrolyte. The charge/
discharge cycles were performed at different rates at room temperature.
The devices were assembled in an argon-filled
glovebox with oxygen and water contents below 1 and 0.1 ppm,
respectively. The Li-ion battery tests were performed by either a
Bio-Logic VMP3 battery tester or an MTI battery analyzer.