LR726 battery.Research and development of new non-flammable and safer lithium batteries

　　Lithium-ion batteries are powering many appliances, from laptops to lawn mowers. But because they rely on flammable components, lithium-ion batteries are prone to burning when damaged. Now, researchers report that they have redesigned these batteries to take advantage of materials that are less likely to burn. On top of that, the new batteries may even store more power than existing models. Gleb Yushin, a materials scientist at the Georgia Institute of Technology in Atlanta, who was not involved in the research, said the work is an "absolutely significant advance." If commercialized, this new battery could help keep electric vehicle drivers safe even if they are unfortunately involved in an accident. Lithium-ion batteries contain three main components - two storage electrodes and a liquid organic electrolyte that separates them. During the charge and discharge process, electrolytes transport lithium ions back and forth between the electrodes, but these electrolytes are flammable. In recent years, researchers have attempted to replace these organic electrolytes with solid electrolytes or water-based electrolytes that do not catch fire. But if these water-based batteries operate at more than 1.23 volts (V)—which is even lower than the 1.5V AA battery operates at—the electrode material reacts with the water molecules, breaking them into hydrogen and oxygen. Usually results in an explosion. However, when the researchers kept the operating voltage below a threshold of 1.23V, the resulting battery stored far less energy than traditional lithium-ion batteries, which operate at about 4V. In 2015, a research team led by Chunsheng Wang, a materials scientist at the University of Maryland, College Park, reported that they had developed a new salt-rich water-based electrolyte. This salty water electrolyte (WiSE) encourages the formation of a protective solid barrier around the electrodes, which prevents the electrodes from tearing apart water molecules inside the electrolyte. But the electrode materials in these batteries can only reach an operating voltage of 3V. In 2017, the future looked bright when Wang Chunsheng and his colleagues reported that they had developed a cathode material that was compatible with 4V and could work with WiSE. All that remains is to deal with the negatively charged electrodes. Now, Wang Chunsheng and his colleagues have achieved this. They reported May 8 in the journal Nature that they have developed a graphite-based cathode that can work with WiSE at 4V or higher. The new electrode materials include bromine and chlorine, which protect the reactive electrode material from water-based electrolytes by locking it in solid salt particles around the electrode. The lithium in the battery is wrapped by solid lithium-bromine and lithium-chloride salt particles around a graphite electrode composed of layers of carbon atoms. When the battery charges, bromine and chlorine atoms abandon the lithium atoms, handing electrons to the cathode and wedged between layers of graphitic carbon, forming another compact solid. The voltage difference between the two electrodes then drives the positively charged lithium ions through the water-based electrolyte to the anode, where they meet electrons provided by an external circuit. When the battery discharges during use, the lithium ions give up these electrons and flow toward the cathode instead. The electrons travel back through an external circuit to the cathode, where bromine and chlorine atoms grab onto them. These charges diffuse out of the graphite. The lithium ions then grab onto them, reforming the solid salt particles, which stay in place until the next round of charging. Wang Chunsheng and his colleagues noticed that their cathode material was already able to store about 30% more charge than traditional cathode materials. But it remains to be seen whether full cells, including the new electrolyte, can ultimately store more energy than commercial batteries. The new WiSE batteries will not require cobalt, a toxic metal found in traditional lithium-ion cathodes. In the Democratic Republic of Congo, cobalt mining has been linked to widespread deaths of miners, often children. The Democratic Republic of Congo is relatively rich in cobalt. The new batteries are not only safer for consumers, but also safer for miners and the environment.

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