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Thin film lithium ion batteries are similar to
![](http://upload.wikimedia.org/wikipedia/commons/thumb/1/12/Schematic_of_Thin_Film_Lithium_Ion_battery.jpg/500px-Schematic_of_Thin_Film_Lithium_Ion_battery.jpg)
Background
Components of Thin Film Battery
Cathode materials
Cathode materials in thin film lithium ion batteries are the same of what is seen in classical lithium ion batteries. They are normally metal oxides that are deposited as a film by various methods.
Metal oxide materials are shown below as well as their relative specific capacities (Λ), open circuit voltages (Voc), and energy densities (DE).
Deposition methods for cathode materials
There are various methods being used in order to deposit a thin film cathode material onto the current collector.
Pulsed Laser Deposition (PLD)
In
Magnetron Sputtering
In Magnetron Sputtering the substrate is cooled for deposition.
Chemical Vapor Deposition (CVD)
In
Sol-Gel Processing
Electrolyte
The greatest difference between classical lithium ion batteries and thin, flexible, lithium ion batteries is in the
Separator Material
Separator materials in lithium ion batteries must have the ability to transport ions through their porous membranes while maintaining a physical separation between the anode and cathode materials in order to prevent short-circuiting. In a thin film based system, the electrolyte is normally a solid electrolyte, capable of conforming to the shape of the battery. Typically this material is a polymer based material and as mentioned above, this polymer commonly acts as both the separator and electrolyte. Since thin film batteries are made of all solid materials, this affords to use of simpler separator materials in these systems such as Xerox paper rather than in liquid based Li-ion batteries.
Current Collector
Current collectors in thin film batteries must be flexible, have high surface area, and cost-effective. Silver nanowires with improved surface area and loading weight have been shown to work as a current collector in these battery systems, but still are not as cost-effective as desired. Extending graphite technology to lithium ion batteries, solution processed
Advantages and Challenges
![](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f0/Ragone_Plot_for_diff_Li_batteries.jpg/300px-Ragone_Plot_for_diff_Li_batteries.jpg)
Thin film lithium ion batteries offer improved performance by having a higher average output voltage, lighter weights thus higher energy density, and longer cycling life than typical rechargeable batteries. In the thin film lithium ion battery, both electrodes are capable of reversible lithium insertion, thus forming a Li-ion transfer cell. Li-ion transfer cells are the most promising systems for satisfying the demand of high specific energy and high power. In order to construct a thin film battery it is necessary to fabricate all the battery components, as an anode, a solid electrolyte, a cathode and current leads into multi-layered thin films by suitable technologies.
In a thin film based system, the electrolyte is normally a solid electrolyte, capable of conforming to the shape of the battery. This is in contrast to classical lithium ion batteries, which normally have liquid electrolyte material. Liquid electrolytes can be challenging to utilized if they are not compatible with the separator. Also liquid electrolytes in general call for an increase in the overall volume of the battery, which is not ideal for designing a system that has high energy density. Additionally, in a thin film flexible Li-ion battery, the electrolyte, which is normally polymer-based, can act as the electrolyte, separator, and binder material. This provides the ability to have flexible systems since the issue of electrolyte leakage is circumvented. Finally, solid systems can be packed together tightly which affords an increase in energy density when compared to classical lithium ion batteries.
Separator materials in lithium ion batteries must have the ability to transport ions through their porous membranes while maintaining a physical separation between the anode and cathode materials in order to prevent short-circuiting. Furthermore, the separator must be resistant to degradation during the battery’s operation. In a thin film Li-ion battery, the separator must be a thin and flexible solid. Typically today, this material is a polymer-based material. Since thin film batteries are made of all solid materials, allows one to use simpler separator materials in these systems such as Xerox paper rather than in liquid based Li-ion batteries.
Scientific Development
Development of thin solid state batteries allows for roll to roll type production of batteries which would decrease production costs. Solid-state batteries can also afford increased energy density due to decrease in overall device weight. Where as the flexible nature allows for novel battery design and incorporation into electronics. Development is still required in cathode materials which will resist decreased capacity due to cycling.
Prior Technology | Replacement Technology | Result |
---|---|---|
Solution based electrolyte | Solid state electrolyte | Increased safety and cycle life |
Polymer separator | Paper separator | Decreased cost increased increased rate of ion conduction |
Metallic current collectors | Carbon nanotube current collectors | Decreased device weight, increased energy density |
Graphite anode | Carbon nanotube anode | Decreased device complexity |
Applications
The advancements made to the thin film lithium ion battery have allowed for many potential applications. The majority of these applications are aimed at improving the currently available consumer and medical products. Thin film lithium ion batteries can be used to make thinner portable electronics, because the thickness of the battery required to operate the device can be reduced greatly. These batteries have the ability to be an integral part of implantable medical devices, such as
Solar Cell Storage Devices
The thin film lithium ion battery can serve as a storage device for the energy collected from a solar cell. These batteries can be made to have a low self discharge rate, which means that these batteries can be stored for long periods of time without a major loss of the energy that was used to charge it. These fully charged batteries could then be used to power some or all of the other potential applications listed below.
Smart Cards
RFID tags
Implantable Medical Devices
Implantable medical devices require batteries that can deliver a steady, reliable power source for as long as possible. These applications call for a battery that has a low self-discharge rate, for when it’s not in use, and a high power rate, for when it needs to be used, especially in the case of an implantable
Wireless Sensors
Wireless sensors need to be in use for the duration of their application, whether that may be in package shipping or in the detection of some unwanted compound, or controlling inventory in a warehouse. If the wireless sensor can’t transmit its data due to low or no battery power, the consequences could potentially be severe based on the application. Also, the wireless sensor must be adaptable to each application. Therefore the battery must be able to fit within the designed sensor. This means that the desired battery for these devices must be long-lasting, size specific, low cost, if they are going to be used in disposable technologies, and must meet the requirements of the data collection and transmission processes. Once again, thin film lithium ion batteries have shown the ability to meet all of these requirements.
Thinner Electronics
The reduction of the battery footprint can be the foothold to thinner and lighter electronics based on these thin film flexible lithium ion batteries. Since the batteries have such a high energy density in such a thin film, a thin film battery can replace a thicker, heavier, less energy dense battery in order to accomplish the same task. Today’s society is fast-moving, technology driven and ever interconnecting. These thinner, lighter electronic devices can help shape the future of the way we use and think about technology. With other technological advancements being made, the possibility of even smaller, thinner and lighter electronic devices than those currently found today is not as far away as was once thought. These developments may be the step that leads to some part of the technology seen in futuristic television shows and movies, like Avatar, for example.
See Also
- Lithium Ion Battery
References
- ^ a b c "Thin, Flexible Secondary Li-Ion Paper Batteries". ACS Nano. 4: 5843–5848. 2010.
- ^ "Characteristics of a New Type of Solid-State Electrolyte with LiPON Interlayer for Li-Ion Thin Film Batteries". Solid State Ionics. 181: 902–906. 2010.
- ^ "Thin-Film Rechargeable Li-Ion Batteries". Solid State Division of Oak Ridge National Lab. 1995.
- ^ "Solid state thin-film lithium battery systems". Solid State & Materials Science: 479–482. 2008.
- ^ The Electrochemical Society Interface. 4: 44–48. 2008.
- ^ "http://www.excellatron.com/smartcards.htm". Excellatron.
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