Thin film rechargeable lithium battery
Encyclopedia
Thin film lithium ion batteries are similar to lithium-ion batteries, but they are composed of thin materials, some only nanometers or micrometers thick, which allow for the finished battery to be just millimeters thick. They have been developed and advanced primarily within the last decade. These batteries consist of a substrate, electrolyte
, current collector, anode
, cathode
, and a charge separator. There has been much research into the determination of the most effective components for this type of battery. It has been shown recently that even ordinary printer paper can be used as a charge separator and a substrate. These thin film batteries are an improvement on the common secondary, or rechargeable, lithium ion batteries in many ways. These batteries exhibit the same voltage
and current as their bulky counterparts, but their thinner dimensions allow for greater applications such as making thinner electronic devices, like cell phones and laptops and even implantable medical devices and reducing the weight of common devices that are run on battery power because of the batteries’ high energy density. These batteries can be formed into any shape and they can be stacked, to be used in parallel, thus even further reducing the space needed for a battery.
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).
materials are fabricated with varying parameters such as laser energy and fluence, substrate temperature, background pressure, and target-substrate distance.
the substrate is cooled for deposition.
volatile precursor materials is deposited onto a substrate material.
material used. Progress in lithium ion batteries relies as much on improvements in the electrolyte as it does in the electrode materials, as the electrolyte plays a major role in safe battery operation.
The concept of thin film lithium ion batteries was increasingly motivated by manufacturing advantages presented by the polymer technology for their use as electrolytes. Lipon, lithium phosphorus oxynitride, is an amorphous polymer
material used as an electrolyte material in thin film flexible batteries. Layers of Lipon are deposited over the cathode material at ambient temperatures by RF magnetron sputtering. This forms the solid electrolyte used for ion conduction between anode and cathode.
Solid polymer electrolytes offer several advantages in comparison to a classical liquid lithium ion battery. Rather than having separate components of electrolyte, binder, and separator, these solid electrolytes can act as all three. This increases the overall energy density of the assembled battery because the constituents of the entire cell are more tightly packed.
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.
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.
, or RFID, tags and wireless sensors. They can also serve as a way to store energy collected from solar cells or other harvesting devices. Each of these applications is possible because of the flexibility in the size and shape of the batteries. The size of these devices does not have to revolve around the size of the space needed for the battery anymore. The thin film batteries can be attached to the inside of the casing or in some other convenient way. The opportunities in which to use this type of batteries are endless.
. 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.
(RFID) tags can be used in many different applications. These tags can be used in packaging, inventory control, used to verify authenticity and even allow or deny access to something. These ID tags can even have other integrated sensors to allow for the physical environment to be monitored, such as temperature or shock during travel or shipping. Also, the distance required to read the information in the tag depends on the strength of the battery. The farther away you want to be able to read the information, the stronger the output will have to be and thus the greater the power supply to accomplish this output. As these tags get more and more complex, the battery requirements will need to keep up. Thin film lithium ion batteries have shown that they can fit into the designs of the tags because of the flexibility of the battery in size and shape and are sufficiently powerful enough to accomplish the goals of the tag. Low cost production methods, like roll to roll lamination, of these batteries may even allow for this kind of RFID technology to be implemented in disposable applications.
s of LiCoO2
have been synthesized in which the strongest x ray reflection is either weak or missing, indicating a high degree of preferred orientation. Thin film solid state
batteries with these textured
cathode
films can deliver practical capacities at high current densities. For example, for one of the cells 70% of the maximum capacity between 4.2 V and 3 V (approximately 0.2 mAh/cm2) was delivered at a current of 2 mA
/cm2. When cycled at rates of 0.1 mA/cm2, the capacity loss was 0.001%/cycle or less. The reliability and performance of Li LiCoO2 thin-film batteries make them attractive for application in implantable devices such as neural stimulators, pacemaker
s, and defibrillators.
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 defibrillator. Also, users of the product will want a battery that can go through many cycles, so these devices will not have to be replaced or serviced often. Thin film lithium ion batteries have the ability to meet these requirements. The advancement from a liquid to a solid electrolyte has allowed these batteries to take almost any shape without the worry of leaking, and it has been shown that certain types of thin film rechargeable lithium batteries can last for around 50,000 cycles. Another advantage to these thin film batteries is that they can be arranged in series
to give a larger voltage
equal to the sum of the individual battery voltages. This fact can be used in reducing the “footprint” of the battery, or the size of the space needed for the battery, in the design of a device.
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
, current collector, anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
, cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
, and a charge separator. There has been much research into the determination of the most effective components for this type of battery. It has been shown recently that even ordinary printer paper can be used as a charge separator and a substrate. These thin film batteries are an improvement on the common secondary, or rechargeable, lithium ion batteries in many ways. These batteries exhibit the same voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
and current as their bulky counterparts, but their thinner dimensions allow for greater applications such as making thinner electronic devices, like cell phones and laptops and even implantable medical devices and reducing the weight of common devices that are run on battery power because of the batteries’ high energy density. These batteries can be formed into any shape and they can be stacked, to be used in parallel, thus even further reducing the space needed for a battery.
Background
Lithium-ion batteries are similar to disposable lithium batteries but have the ability to be recharged. Also they have high energy density and last longer than many similar battery technologies. In the battery cell lithium ions flow through the electrolyte from the anode to the cathode while the battery is being discharged. Upon recharging the battery the lithium ions move back to the anode. This Li-ion battery design is effective for large devices. However, as a more mobile, technology driven society we rely heavily on portable electronics, which require thin batteries for power. Research into thin film batteries has developed over the recent years to accommodate for this demand.Cathode materials
CathodeCathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
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).
| Λ(Ah/kg) | VOC(V) | DE(Wh/kg) | |
|---|---|---|---|
| LiCoO2 | 145 | 4 | 580 |
| LiMn2O4 | 148 | 4 | 592 |
| LiFePO4 | 170 | 3.4 | 578 |
| DE = Λ VOC |
| Λ: capacity (mAh/g) |
| VOC: Open circuit potential |
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 Pulsed Laser DepositionPulsed laser deposition
Pulsed laser deposition is a thin film deposition technique where a high power pulsed laser beam is focused inside a vacuum chamber to strike a target of the material that is to be deposited...
materials are fabricated with varying parameters such as laser energy and fluence, substrate temperature, background pressure, and target-substrate distance.
Magnetron Sputtering
In Magnetron SputteringSputtering
Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...
the substrate is cooled for deposition.
Chemical Vapor Deposition (CVD)
In Chemical Vapor DepositionChemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
volatile precursor materials is deposited onto a substrate material.
Sol-Gel Processing
Sol-gel processing allows for homogeneous mixing of precursor materials at the atomic level.Electrolyte
The greatest difference between classical lithium ion batteries and thin, flexible, lithium ion batteries is in the electrolyteElectrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
material used. Progress in lithium ion batteries relies as much on improvements in the electrolyte as it does in the electrode materials, as the electrolyte plays a major role in safe battery operation.
The concept of thin film lithium ion batteries was increasingly motivated by manufacturing advantages presented by the polymer technology for their use as electrolytes. Lipon, lithium phosphorus oxynitride, is an amorphous polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
material used as an electrolyte material in thin film flexible batteries. Layers of Lipon are deposited over the cathode material at ambient temperatures by RF magnetron sputtering. This forms the solid electrolyte used for ion conduction between anode and cathode.
Solid polymer electrolytes offer several advantages in comparison to a classical liquid lithium ion battery. Rather than having separate components of electrolyte, binder, and separator, these solid electrolytes can act as all three. This increases the overall energy density of the assembled battery because the constituents of the entire cell are more tightly packed.
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 carbon nanotubes (CNT) films are being looked into for use as both the current collector and anode material. CNTs have the ability to intercalate lithium and maintain high operating voltages, all with low mass loading and flexibility.Advantages and Challenges
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 rollRoll-to-roll processing
In the field of electronic devices, Roll-to-roll processing, also known as web processing, reel-to-reel processing or R2R, is the process of creating electronic devices on a roll of flexible plastic or metal foil...
type production of batteries which would decrease production costs. Solid-state batteries
Solid-state battery
In solid-state ionics, a solid-state battery is a battery that has both solid electrodes and solid electrolytes. As a group, these materials are very good conductors of ions but are essentially insulating toward electrons, properties that are prerequisites for any electrolyte...
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
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
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 separators Polymer separators A polymer separator is a permeable membrane placed between the anode and cathode of a battery. The main function of a separator is to keep the positive and negative electrodes, the cathode and anode respectively, apart to prevent electrical short circuits while also allowing the transport of ionic... |
Paper separator | Decreased cost 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 defibrillators and neural stimulators, “smart” cards, radio frequency identificationRadio Frequency Identification
Radio-frequency identification is a technology that uses radio waves to transfer data from an electronic tag, called RFID tag or label, attached to an object, through a reader for the purpose of identifying and tracking the object. Some RFID tags can be read from several meters away and beyond the...
, or RFID, tags and wireless sensors. They can also serve as a way to store energy collected from solar cells or other harvesting devices. Each of these applications is possible because of the flexibility in the size and shape of the batteries. The size of these devices does not have to revolve around the size of the space needed for the battery anymore. The thin film batteries can be attached to the inside of the casing or in some other convenient way. The opportunities in which to use this type of batteries are endless.
Solar Cell Storage Devices
The thin film lithium ion battery can serve as a storage device for the energy collected from a solar cellSolar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
. 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
Smart cards are basically the same size as a credit card, but they contain a microchip that can be used to access information, give authorization, or process an application. These cards can go through harsh production conditions, with temperatures in the range of 130 to 150°C, in order to complete the high temperature, high pressure lamination processes. These conditions can cause other batteries to fail because of degassing or degradation of organic components within the battery. Thin film lithium ion batteries have been shown to withstand temperatures of -40 to 150°C. This use of thin film lithium ion batteries is hopeful for other extreme temperature applications.RFID tags
Radio Frequency IdentificationRadio Frequency Identification
Radio-frequency identification is a technology that uses radio waves to transfer data from an electronic tag, called RFID tag or label, attached to an object, through a reader for the purpose of identifying and tracking the object. Some RFID tags can be read from several meters away and beyond the...
(RFID) tags can be used in many different applications. These tags can be used in packaging, inventory control, used to verify authenticity and even allow or deny access to something. These ID tags can even have other integrated sensors to allow for the physical environment to be monitored, such as temperature or shock during travel or shipping. Also, the distance required to read the information in the tag depends on the strength of the battery. The farther away you want to be able to read the information, the stronger the output will have to be and thus the greater the power supply to accomplish this output. As these tags get more and more complex, the battery requirements will need to keep up. Thin film lithium ion batteries have shown that they can fit into the designs of the tags because of the flexibility of the battery in size and shape and are sufficiently powerful enough to accomplish the goals of the tag. Low cost production methods, like roll to roll lamination, of these batteries may even allow for this kind of RFID technology to be implemented in disposable applications.
Implantable Medical Devices
Thin filmThin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
s of LiCoO2
Lithium cobalt oxide
Lithium cobalt oxide is a chemical compound commonly used in the positive electrodes of lithium-ion batteries. The structure of LiCoO2 is known theoretically and has been confirmed with techniques like x-ray diffraction, electron microscopy, neutron powder diffraction, and EXAFS: it consists of...
have been synthesized in which the strongest x ray reflection is either weak or missing, indicating a high degree of preferred orientation. Thin film solid state
Solid-state chemistry
Solid-state chemistry, also sometimes referred to as materials chemistry, is the study of the synthesis, structure, and properties of solid phase materials, particularly, but not necessarily exclusively of, non-molecular solids...
batteries with these textured
Texture (crystalline)
In materials science, texture is the distribution of crystallographic orientations of a polycrystalline sample. A sample in which these orientations are fully random is said to have no texture. If the crystallographic orientations are not random, but have some preferred orientation, then the...
cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
films can deliver practical capacities at high current densities. For example, for one of the cells 70% of the maximum capacity between 4.2 V and 3 V (approximately 0.2 mAh/cm2) was delivered at a current of 2 mA
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
/cm2. When cycled at rates of 0.1 mA/cm2, the capacity loss was 0.001%/cycle or less. The reliability and performance of Li LiCoO2 thin-film batteries make them attractive for application in implantable devices such as neural stimulators, pacemaker
Pacemaker
An artificial pacemaker is a medical device that uses electrical impulses to regulate the beating of the heart.Pacemaker may also refer to:-Medicine:...
s, and defibrillators.
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 defibrillator. Also, users of the product will want a battery that can go through many cycles, so these devices will not have to be replaced or serviced often. Thin film lithium ion batteries have the ability to meet these requirements. The advancement from a liquid to a solid electrolyte has allowed these batteries to take almost any shape without the worry of leaking, and it has been shown that certain types of thin film rechargeable lithium batteries can last for around 50,000 cycles. Another advantage to these thin film batteries is that they can be arranged in series
Series and parallel circuits
Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur very frequently. Components connected in series are connected along a single path, so the same current flows through all of the...
to give a larger voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
equal to the sum of the individual battery voltages. This fact can be used in reducing the “footprint” of the battery, or the size of the space needed for the battery, in the design of a device.