Scientists at the DOE’s Argonne National Lab have developed a new cathode coating by using an oxidative chemical vapor deposition technique that can help keep the cathode electrically and ionically conductive, ensure safety after many cycles, and help with other challenges as well. The findings are reported in the May online edition of Nature Energy.
“The coating we’ve discovered really hits five or six birds with one stone,” said report author and Argonne battery scientist Khalil Amine.
In the research, Amine and his fellow researchers took particles of Argonne’s nickel-manganese-cobalt (NMC) cathode material and encapsulated them with a sulfur-containing polymer called PEDOT. This polymer provides the cathode with a layer of protection from the battery’s electrolyte as the battery charges and discharges.
Unlike conventional coatings, which only protect the exterior surface of the micron-sized cathode particles and leave the interior vulnerable to cracking, the PEDOT coating has the ability to penetrate to the cathode particle’s interior, adding an additional layer of shielding.
Although PEDOT prevents the chemical interaction between the battery and the electrolyte, it still allows for the transport of lithium ions and electrons that the battery requires in order to function.
“This coating is essentially friendly to all of the processes and chemistry that makes the battery work and unfriendly to all of the potential reactions that would cause the battery to degrade or malfunction,” said primary report author and Argonne chemist Guiliang Xu.
The coating also largely prevents the cathode material from converting to another form called spinel, which causes the battery’s cathode to deactivate. “The combination of almost no spinel formation with its other properties makes this coating a very exciting material,” Amine said.
The PEDOT material also demonstrated the ability to prevent oxygen release, a major factor for the degradation of NMC cathode materials at high voltage. “This PEDOT coating was also found to be able to suppress oxygen release during charging, which leads to better structural stability and also improves safety,” Amine said.
Amine indicated that battery scientists could likely scale up the coating for use in nickel-rich NMC-containing batteries. “This polymer has been around for a while, but we were still surprised to see that it has all of the encouraging effects that it does,” he said.
With the coating applied, the researchers believe that the NMC-containing batteries could either run at higher voltages – thus increasing their energy output – or have longer lifetimes, or both.
Source: Argonne National Laboratory