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A thin film battery is a form of lithium ion battery that can be as small as a few millimeters thick. Thin film batteries use a process similar to that of a standard lithium ion battery to provide power, but have several advantages over the larger battery. In addition to being much smaller, they also last longer, can operate under more extreme temperatures, and can be formed into any shape. They were developed by a team of scientists and engineers led by Dr. John Bates at Oak Ridge National Laboratory in Tennessee.
The method used to make a battery that is thinner than a United States quarter is a process called physical vapor deposition. The materials for the thin film battery are layered one at a time onto a substrate. If the substrate is flexible, the battery will be flexible as well. Each material starts as a vapor, which is then condensed to form a thin, solid coating on the substrate. The substrate is necessary to separate the anode and the cathode in the battery.
An anode is the contact point on the battery that the current flows into. The cathode is the point it flows out of. All types of lithium ion batteries, including the thin film battery, work when a lithium ion moves from the anode to the cathode through a solid electrolyte. An electrolyte is any material that conducts electricity. In a thin film battery, the electrolyte is often a flexible polymer.
Like all lithium ion batteries, thin film batteries are rechargeable. Lithium ion batteries are common in consumer electronics like cellular phones and laptops. As a thin film battery is so small, the electronic device that it powers can be small as well. This allows for electronics that are smaller and lighter than ones powered using standard lithium ion batteries.
Besides its size, the thin film battery has several other advantages over a standard lithium ion battery. It has a better energy-to-weight ratio. The cost of the battery does not increase as the size decreases. Thin film batteries can also function in extreme temperatures that would damage standard lithium ion batteries.
A thin film battery has a longer cycle life than a standard lithium ion battery. The life cycle of a battery is the number of times it can be charged and then completely discharged before its energy capacity falls below 80 percent of the original capacity. This loss of power happens because the materials in the battery break down very slowly as electricity moves through them.
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