First-principles investigation of the gas evolution from the cathodes of lithium-ion batteries during the storage test

Gas evolution related to the positive electrode of charged lithium-ion batteries during the storage test was investigated using a first-principle method. The distribution of lithium during the delithiation process was simulated based on the density functional theory calculations of the energy required to remove the lithium from the surface or bulk crystal of lithium nickel cobalt manganese oxide (NCM) and lithium cobalt oxide (LCO). Lithium coverage of the surface was smaller for LCO than NCM at a highly charged state. The energy required to form an oxygen vacancy in NCM and LCO crystal was also calculated. The results showed that LCO was more apt to emit oxygen than NCM as the delithiation percentage was increased. The results suggest that the gas-generating side reactions related to the emission of oxygen would be more significant for LCO with high voltage charging. Experimental result showed a considerable portion of the gas was generated at the initial stages of storage for NCM, whereas LCO showed slow but steady gas evolution with increasing storage time. A large amount of Li2CO3 or LiOH on the surface of NCM appears to cause an immediate gas-generating side reaction, whereas LCO produces slow side reaction related to the emission of oxygen from the LCO material itself.