New imaging technique sees inside lithium batteries
The image looks like something out of a SciFi movie: metal flows out of one spot, reaching towards its companion piece opposite, growing little fingers to explore its surroundings. But this is not SciFi, it is real life.
This is what it looks like when lithium electrodes are used in a lithium-ion battery. The lithium metal crystal structure experiences stress as it cycles through discharges and recharges. This stress forces parts of the metal to extrude away from the body of the electrode. It is a common phenomenon, especially in pure metals carrying electrical charges, known as dendrite formation.
When the dendrites bridge the gap between the anode and the cathode, a short circuit occurs. In the best case, the battery life is shortened. In the worst, the battery starts heating itself up until the point of danger: a fire or explosion can occur.
In theory a pure lithium electrode would be the ideal electrode for a lithium-ion battery because of the favorable properties of lithium metal and because it allows a cycle of lithium ions into the solid (metal) and back into solution (lithium ions) again during use and recharging.
Dendrites give battery engineers big headaches which they try to resolve by using clever alternative materials for the electrodes or additives in the electrolyte. But slow, laborious and often destructive analytical methods delay the experimental feedback necessary to finding better materials and optimizing battery lifespan and safety.
The news of a real-time, in situ, 3-D imaging method developed by scientists at the Department of Chemistry of New York University spurs hopes that we will witness break-throughs in battery technology as researchers can immediately see what is happening inside batteries. This technique may also be useful in the emerging field of battery safety testing, which becomes increasingly necessary as a spate of battery incidents has led to restrictions of devices on airplanes and consumer fears about the products containing these batteries, ranging from Samsung Galaxy Note 7 smartphones to Tesla electric cars.
The chemists achieved the speed necessary for real-time imaging by looking not at the dendrites but at the electrolyte in the space around them. The distortions around the dendrites on the MRI images act like "shadows" that can be used to visualize the dendrites that cast the shadow.
The other methods in use to examine dendrites usually involve opening the battery up, which disturbs the chemistry and the delicate dendrite structures. And, of course, these methods are useless for seeing what is happening when the batteries are in use.
As our future seems dependent on a myriad of devices powered by batteries, especially as these batteries start to give us more independence from fossil fuels, any advance in the science of better batteries and battery safety will be welcome.