19-04-2013, 04:54 PM
Bendable Inorganic Thin-Film Battery for Fully Flexible Electronic
Systems
[attachment=53211]
ABSTRACT:
High-performance flexible power sources have gained attention, as they enable the realization of next-generation
bendable, implantable, and wearable electronic systems. Although the rechargeable lithium-ion battery (LIB) has been regarded
as a strong candidate for a high-performance flexible energy source, compliant electrodes for bendable LIBs are restricted to only
a few materials, and their performance has not been sufficient for them to be applied to flexible consumer electronics including
rollable displays. In this paper, we present a flexible thin-film LIB developed using the universal transfer approach, which enables
the realization of diverse flexible LIBs regardless of electrode chemistry. Moreover, it can form high-temperature (HT) annealed
electrodes on polymer substrates for high-performance LIBs. The bendable LIB is then integrated with a flexible light-emitting
diode (LED), which makes an all-in-one flexible electronic system. The outstanding battery performance is explored and well
supported by finite element analysis (FEA) simulation.
Introduction
The advent of a fully flexible electronic system will be a
great leap in technology, as it will open the door to the
next-generation electronic environment based on bendable,
implantable, and wearable devices. These next-generation
electronic devices are marked by unprecedented advantages
of excellent portability, lightweight, and conformal contact on
curvilinear surfaces.1,2 Although the remarkable development of
mechanically flexible electronic devices has been widely
reported, their feasibility has been restricted in unit
components, such as light-emitting diodes (LEDs),3,4 sensing
electrodes,5,6 circuit elements,7−9 and radio frequency identification
(RFID) antennas.10 Toward all-in-one flexible systems,
the development of a bendable high-power source that can be
applied to consumer electronics has been an obstacle to
overcome.Rechargeable lithium ion batteries (LIBs) have shown great
promise as flexible power sources due to their high operating
voltage, high energy capacity, and long-term cyclability.2,11 In
recent years, compliant materials on curvilinear surfaces, such as
carbon nanotubes,12−15 carbon nanofibers,16 graphene,17,18
metal oxide-based nanowires,19 and slurry-typed mixtures of
nanostructured active materials,20,21 have been explored as
flexible LIB electrodes. Although they have shown advanced
performance for flexible LIBs, the combination of these as
anode or cathode has only been accessible to a few electrode
materials that are synthesizable in certain nanostructures or
carbon templates.22 Moreover, the use of liquid-type electrolytes
has added more complexities in the realization of a fully
flexible LIB, and their thermal stability should be carefully
considered.
Figure 1a shows the robustness of a flexible LIB turning on a
blue LED in bent condition. The employment of high
electrochemical potential materials, as depicted in the inset,
leads to the maximum charging voltage of 4.2 V and the specific
capacity of 106 μAh/cm2 (discharge capacity of 683 μAh) at a
rate of 46.5 μA/cm2 under polydimethylsiloxane (PDMS)
polymer wrapping (2.54 × 2.54 × 0.2 cm3), which indicates
higher performance than that of previously reported flexible
LIBs based on nanosized materials.12−21 The construction of
the bendable thin-film battery starts with a standard fabrication
process upon a brittle mica substrate. A cathode current
collector (CCC), a lithium cobalt oxide cathode (LiCoO2;
high-temperature (HT) annealing of LiCoO2 at 700 °C), a
lithium phosphorus oxynitride electrolyte (LiPON), a lithium
(Li) metal anode, and protective encapsulation multilayers were
sequentially deposited on the substrate (Figure 1b-i). LiCoO2
has received great interest from many researchers due to its
high operating potential of ∼4 V and high reversible capacity,
and is currently the most widely used cathode in LIB.25−27
Although advanced cathode materials having high capacity and
potential have been recently developed, LiCoO2 is still regarded
as the most reliable cathode material. As is the case for any
other electrode materials, it should be noted that the HT
annealing process for the crystallinity of LiCoO2 material is a
crucial step to realize the high- performance solid-state LIB. It is
because the solid-state lithium diffusion is critically hindered by
any imperfections in the crystal.
Systems
[attachment=53211]
ABSTRACT:
High-performance flexible power sources have gained attention, as they enable the realization of next-generation
bendable, implantable, and wearable electronic systems. Although the rechargeable lithium-ion battery (LIB) has been regarded
as a strong candidate for a high-performance flexible energy source, compliant electrodes for bendable LIBs are restricted to only
a few materials, and their performance has not been sufficient for them to be applied to flexible consumer electronics including
rollable displays. In this paper, we present a flexible thin-film LIB developed using the universal transfer approach, which enables
the realization of diverse flexible LIBs regardless of electrode chemistry. Moreover, it can form high-temperature (HT) annealed
electrodes on polymer substrates for high-performance LIBs. The bendable LIB is then integrated with a flexible light-emitting
diode (LED), which makes an all-in-one flexible electronic system. The outstanding battery performance is explored and well
supported by finite element analysis (FEA) simulation.
Introduction
The advent of a fully flexible electronic system will be a
great leap in technology, as it will open the door to the
next-generation electronic environment based on bendable,
implantable, and wearable devices. These next-generation
electronic devices are marked by unprecedented advantages
of excellent portability, lightweight, and conformal contact on
curvilinear surfaces.1,2 Although the remarkable development of
mechanically flexible electronic devices has been widely
reported, their feasibility has been restricted in unit
components, such as light-emitting diodes (LEDs),3,4 sensing
electrodes,5,6 circuit elements,7−9 and radio frequency identification
(RFID) antennas.10 Toward all-in-one flexible systems,
the development of a bendable high-power source that can be
applied to consumer electronics has been an obstacle to
overcome.Rechargeable lithium ion batteries (LIBs) have shown great
promise as flexible power sources due to their high operating
voltage, high energy capacity, and long-term cyclability.2,11 In
recent years, compliant materials on curvilinear surfaces, such as
carbon nanotubes,12−15 carbon nanofibers,16 graphene,17,18
metal oxide-based nanowires,19 and slurry-typed mixtures of
nanostructured active materials,20,21 have been explored as
flexible LIB electrodes. Although they have shown advanced
performance for flexible LIBs, the combination of these as
anode or cathode has only been accessible to a few electrode
materials that are synthesizable in certain nanostructures or
carbon templates.22 Moreover, the use of liquid-type electrolytes
has added more complexities in the realization of a fully
flexible LIB, and their thermal stability should be carefully
considered.
Figure 1a shows the robustness of a flexible LIB turning on a
blue LED in bent condition. The employment of high
electrochemical potential materials, as depicted in the inset,
leads to the maximum charging voltage of 4.2 V and the specific
capacity of 106 μAh/cm2 (discharge capacity of 683 μAh) at a
rate of 46.5 μA/cm2 under polydimethylsiloxane (PDMS)
polymer wrapping (2.54 × 2.54 × 0.2 cm3), which indicates
higher performance than that of previously reported flexible
LIBs based on nanosized materials.12−21 The construction of
the bendable thin-film battery starts with a standard fabrication
process upon a brittle mica substrate. A cathode current
collector (CCC), a lithium cobalt oxide cathode (LiCoO2;
high-temperature (HT) annealing of LiCoO2 at 700 °C), a
lithium phosphorus oxynitride electrolyte (LiPON), a lithium
(Li) metal anode, and protective encapsulation multilayers were
sequentially deposited on the substrate (Figure 1b-i). LiCoO2
has received great interest from many researchers due to its
high operating potential of ∼4 V and high reversible capacity,
and is currently the most widely used cathode in LIB.25−27
Although advanced cathode materials having high capacity and
potential have been recently developed, LiCoO2 is still regarded
as the most reliable cathode material. As is the case for any
other electrode materials, it should be noted that the HT
annealing process for the crystallinity of LiCoO2 material is a
crucial step to realize the high- performance solid-state LIB. It is
because the solid-state lithium diffusion is critically hindered by
any imperfections in the crystal.