Argonne National Laboratory (ANL) has developed a Coin Cell NMR/MRI Imager that can analyze thin films and membranes (such as those in a coin cell battery) in real time, under real test conditions, through a complete battery charge/discharge cycling process.
The process provides three simultaneous views of complementary information never before available to battery researchers.
The ANL imager is a simple device that combines the function of a nuclear magnetic resonance (NMR)/magnetic resonance imaging (MRI) detector, an electrochemical cell, and a video camera. The device can be used as a stand-alone electrochemical device or with NMR/MRI, video, temperature, and/or pressure add-ons.
The multipurpose device can perform in situ, real-time analyses of thin films by NMR spectroscopy, MRI imaging, electrochemistry measurements, and video imaging, and can be used for electrochemical synthesis of novel film/membrane materials.
The device's unique NMR/MRI capability is the result of a design twist that turns a problem into a solution. The Argonne Coin Cell NMR/MRI Imager is composed of a coin cell press, principal detector element (PDE), and the internal components of an electrochemical cell.
The PDE is a flat metal conductor that simultaneously serves as the NMR detector element and the current collector for the cathode or anode electrode in the electrochemical cell. The PDE is connected at opposite ends to metal conductor rods that form part of an electromagnetic resonator circuit. A cylindrical metallic container houses the detector element and conductor rods, and forms part of a complete radio frequency current. This design is what enables the device's unique NMR/MRI capability, allowing the analysis of active thin films and membranes.
What this means is that—for the first time—a film or membrane, such as the as-manufactured working components of a coin cell battery, can be analyzed directly ("as is") by being placed on a flat circular detector.
Turning a Problem Into a Solution
You can't do NMR/MRI if metal is involved, so how can the Argonne Coin Cell NMR/MRI Imager record NMR spectra and MRI images?
Essentially, the Imager transforms a "show-stopping" problem into a simple, elegant solution. In NMR spectroscopy, a metal detector element—traditionally in coil form—generates information about a sample. But when that sample is metal, such as the steel housing of a coin cell battery, there is an incompatiblity that results in, at best, inaccurate (distorted) or incomplete data and, at worst, sparking that can destroy the NMR coil and the sample.
ANL's device transforms this problem into a solution by using a circular metal disk as the principal detector element. This enables NMR analysis of films or membranes in as-manufactured form under actual test conditions—and, in the case of battery materials, throughout the battery's entire cycling process, a capability not currently offered by any other device.
NMR spectrometry produces a collection of spectra with information on each of the working components (cathode, separator, and anode; see figure on right). The NMR spectra are "sorted out" into separate spectra through one-dimensional MRI—the key that makes the concept work.
Functionality
All three functionalities of the Coin Cell Imager (NMR/MRI, electrochemical, and video) can be illustrated by one application in the important area of the ubiquitous lithium-ion rechargeable battery used by consumers (portable electronic devices such as cell phones and laptop computers, hearing aids, biomedical devices, etc.).
The same type of battery promises to have an even greater impact on providing the energy that will be needed for electric and hybrid-electric vehicles.
For continued advancement in making batteries that are increasingly smaller but more powerful, the development of better battery materials is key. Existing materials impose limitations on the size, power, and life of rechargeable lithium batteries. ANL's coin cell imager is uniquely suited to investigate the battery challenges that impose limitations on size, power, and life.
ANL researchers demonstrated the detector's utility by investigating for the first time the cyclic insertion and extraction of lithium in a carbon mixture that is currently used in commercially available lithium-ion batteries by 7Li NMR spectroscopy under actual operating conditions.
The study of battery challenges under operating conditions is far more useful because the researcher can catch the onset of the problem and follow its progress as the battery is charged and discharged multiple times, and subjected to temperatures above or below ambient.
These conditions mimic the usage of the battery by the consumer, including those times when the cell phone is accidentally left in the car in extremely hot or cold temperatures. The in situ capability of the coin cell battery imager allows researchers to conduct probe experiments throughout a lithium battery's entire cycling process. They can now directly and unambiguously follow the various fractions of lithium ions in different electronic environments.
Argonne's Coin Cell NMR/MRI Imager being held by intern Katarina Ruscic. (Click image to enlarge)
Argonne's Coin Cell NMR/MRI Imager (Click image to enlarge)
