The scientists from the U.S. Department of Energy's (DOE) Argonne National Laboratory have developed a new cathode coating that provides an excellent electro/chemical stability of the battery after many cycles. The paper has been published in Nature Energy.
The organic liquid electrolyte in lithium-ion batteries is flammable and brings dangerous safety risk. The safety is dramatically improved when the liquid electrolyte is replaced by inorganic solid in case of solid-state batteries. Besides this, the solid-state batteries have the potential for improved power and energy density, which is the reason for their appeal as the next generation of batteries. However, this battery type has disadvantages.
The contacts between cathode and electrolyte interface are often unstable and cause high interfacial impedance that increases during battery operation and causes deterioration of cell performance. Coating this interface with another layer significantly improves stability. The researchers used an oxidative chemical vapor deposition technique to make the cathode coating that has the potential to solve several issues with solid-state batteries.
“The coating we’ve discovered really hits five or six birds with one stone,” said Researcher Khalil Amine.
They have encapsulated particles of the nickel-manganese-cobalt (NMC) cathode material with a sulfur-containing polymer, polyethylenedioxythiophene, referred to as PEDOT. A protective conductive polymer, PEDOT skin, is built on layered oxide cathode materials The polymer layer provides the protection against electrolyte during the battery charging and discharging process. The conventional coating only protects the exterior surface of the cathode where the interior is susceptible to cracking, whereas the PEDOT coating penetrates to the interior of the particle of the cathode and provides an additional shield.
The PEDOT allows and facilitates the transport of lithium ions and electrons during normal battery operation but prevents chemical interaction between the battery and the electrolyte and other reactions that degrade or malfunction in the battery. In addition, the coating prevents a process in which the cathode material changes to create a spinel, causing the cathode to deactivate. Also, the PEDOT coating prevents oxygen release during battery charging. The oxygen causes the degradation of the nickel manganese cobalt (NMC) cathode materials at high voltage.
The researchers believe that applying the PEDOT coating brings many advantages, especially for the NMC cathode batteries. They could be used at the higher voltages, which increases the energy output, and therewithal have a longer lifespan.