By Josh Perry, Editor
Engineers from the University of Illinois at Chicago demonstrated how a graphene coating could remove the oxygen from lithium battery fires, providing a layer of safety during thermal runaway, according to a report from the school.
Lithium cobalt oxide particles coated in graphene.
“The reasons lithium batteries catch fire include rapid cycling or charging and discharging, and high temperatures in the battery,” the report said. “These conditions can cause the cathode inside the battery — which in the case of most lithium batteries is a lithium-containing oxide, usually lithium cobalt oxide — to decompose and release oxygen. If the oxygen combines with other flammable products given off through decomposition of the electrolyte under high enough heat, spontaneous combustion can occur.”
Researchers focused on preventing oxygen from leaving the cathode to mix with other flammable products and, based on previous studies, they knew that graphene was impermeable to oxygen atoms. The graphene was altered to make it conduct electricity and then wrapped around the lithium-cobalt oxide cathode.
“When they looked at the graphene-wrapped lithium cobalt oxide particles using electron microscopy, they saw that the release of oxygen under high heat was reduced significantly compared with unwrapped particles,” the article added.
Using a binding material, the researchers formed a usable cathode and incorporated it into a battery. During battery cycling tests, they saw almost no oxygen escaping at high voltages and the battery continued to perform after 200 cycles. The battery lost only 14 percent of its capacity, which was three times better than conventional batteries.
The research was recently published in Advanced Functional Materials. The abstract read:
“LiCoO2 is a prime example of widely used cathodes that suffer from the structural/thermal instability issues that lead to the release of their lattice oxygen under nonequilibrium conditions and safety concerns in Li?ion batteries.
“Here, it is shown that an atomically thin layer of reduced graphene oxide can suppress oxygen release from LixCoO2 particles and improve their structural stability. Electrochemical cycling, differential electrochemical mass spectroscopy, differential scanning calorimetry, and in situ heating transmission electron microscopy are performed to characterize the effectiveness of the graphene?coating on the abusive tolerance of LixCoO2.
“Electrochemical cycling mass spectroscopy results suggest that oxygen release is hindered at high cutoff voltage cycling when the cathode is coated with reduced graphene oxide. Thermal analysis, in situ heating transmission electron microscopy, and electron energy loss spectroscopy results show that the reduction of Co species from the graphene?coated samples is delayed when compared with bare cathodes. Finally, density functional theory and ab initio molecular dynamics calculations show that the rGO layers could suppress O2 formation more effectively due to the strong C?Ocathode bond formation at the interface of rGO/LCO where low coordination oxygens exist.
“This investigation uncovers a reliable approach for hindering the oxygen release reaction and improving the thermal stability of battery cathodes.”