Batteries Go to The Doctor Too
Batteries see specialists and undergo tests just like people
When a person becomes ill and cannot function in their everyday life, they pay a visit to a doctor to find the problem and get treatment. Some Energy Frontiers Research Centers (EFRCs) act like a hospital for batteries. There are many EFRCs dedicated to electrical energy storage such as NorthEast Center for Chemical Energy Storage (NECCES) and Center for Electrochemical Energy Science (CEES). In the study of lithium-ion batteries for energy storage, EFRC researchers from multiple fields collaborate to understand what troubles their patients.
The lithium ion battery is a trending research topic because of its use in portable electronics and its role in capturing energy from renewable resources. Just like a person, a battery is a complex system of components that need to work together to optimize performance during its lifetime. All batteries are made of two primary components: a positive electrode (cathode) and a negative electrode (anode) sandwiched between an electrolyte. When a lithium ion battery powers a device, the lithium ions move from the anode through the electrolyte to the cathode (discharging the battery). Likewise, when we store energy through charging, an outside force will shuttle lithium ions from the cathode back to the anode. Although this concept seems quite simple, batteries undergo complex chemical reactions that researchers study in order to understand and improve. Before researchers can make a battery charge faster, last longer and be safer, they need to expose batteries to a whole series of examinations.
Just as medical students study cadavers, researchers dissect batteries to study their parts. Most measurements on battery components are done post mortem because certain characterization techniques have limitations. Battery casings are manufactured to be thick for safety and can impede spectroscopy measurements. For instance, electron spectroscopy probes can provide valuable chemical information but are limited to detecting signals from the surface so the battery needs to be disassembled for such measurements. Many unique and/or unwanted reactions can occur at the surface of electrodes, also known as the electrode interface because of its contact with the electrolyte within the battery. By dissecting the battery and studying the local chemistry, researchers can determine the affinity of such reactions and how the interface plays an important role in battery efficiency.
Surface chemistry can be, and often is, extremely different compared to the bulk chemistry of an electrode. This is in part due to reactions that are likely to start at the surface and propagate to the bulk — or not at all. In order to investigate the bulk chemistry, researchers use X-rays as a probe in addition to utilizing surface sensitive spectroscopy techniques. By tuning the X-ray energy, researchers can induce X-ray absorption in any material and observe the arrangement of its atoms. High energy X-rays are very penetrating and even allow researchers to measure a battery while it is running. This makes characterization non-intrusive and reduces the need to dissect the battery. Similarly, there are non-intrusive medical techniques being used today in diagnosing a person. Taking an X-ray of a person’s arm after an accident will reveal any fractured bones. This is due to the calcium in their bones being more absorbing than skin or muscle tissue. This cartoon depicts a lithium ion battery getting examined by X-rays while it is cycling.
Continuing the analogy, medical professionals occasionally perform a cardiopulmonary exercise test (CPET) on their patients to measure their breathing during strenuous exercise. Similarly, researchers can characterize gas evolution in a battery while it is running. Many battery materials will exert gases such as hydrogen, oxygen or carbon dioxide, either intentionally or as a result of instability through stress. By observing the gas evolution of a battery as it is being stressed, researchers can pinpoint the moment of instability when side reactions occur. This cartoon depicts a battery undergoing a CPET exam while it is ‘running’.
Once tests are complete and diagnoses are made, medical doctors prescribe medicine to their patients for treatment. Likewise, researchers can propose solutions to improve the performance of a battery. Just like there can be multiple drugs to treat a patient, there are multiple ways to improve battery performance. One such method is to make the material smaller — even down to the nanoscale. For example, in lithium ion batteries, nano-sizing the anode and cathode materials reduces the distance lithium has to travel. One way to achieve this is by aggressively smashing these materials into smaller pieces. Just as medicines can present side effects, this aggressive smashing can lead to impurities that are detrimental to a battery. If a material is very insulating, it can be mixed with carbon to improve electrical conductivity. Materials that exhibit instability during cycling can see improved performance after substituting in other elements. Many of these solutions are industry standards.
Just like there are many different types of batteries each having their own unique chemistry, a person has their own unique chemistry. It is up to research specialists to find the best ways to treat them. Just like there are new examination procedures and drugs invented every day; energy storage researchers are developing new characterization techniques as well as new methods to improve current batteries and learn how to make better batteries for the future.