Title : Rational design of battery cathode materials
Abstract:
Current Li ion batteries (LIBs) are improved versions of the 1991 Sony LIB based on graphite anode, organic liquid electrolytes, and LiCoO2 layered oxide cathode. In the commercial applications of LIBs, cathode materials are known to be the critical component in determining the battery cost (~50% of material cost) and the energy storage capacity (cell capacity = ~1/3 cathode capacity). Over the last 30 years, the initial LiCoO2 cathode (~140 mAh/g charge capacity) has evolved to high capacity cathodes with increasing Ni content replacing Co starting from Li(Ni1/3Co1/3Mn1/3)O2 or NCM111 (~160 mAh/g) to NCM433, NCM532, NCM622, NCM721, NCM811 (~200 mAh/g), and LiNiO2 (> 200 mAh/g). With 70-80% Ni in NCM cathodes (theoretical capacity of ~275 mAh/g), more than 70% of Li can be utilized in the electrochemical reactions in realizing the high-capacity cathode. However, in the fully charged state of LIBs, cathode materials are very unstable toward chemical reactions (irreversible reactions with electrolytes, oxygen evolution and phase changes) and mechanical degradation (interface crack formation). Specifically, the high-Ni NCM cathode materials are known to have large volume change (-7%) at 80% delithiation with the majority of volume change (DV/V = -5%) happening at Li delithiation from 70% to 80% leading to the mechanical cracking of the secondary cathode particles. In this talk, we will discuss multiscale modeling study based on density functional theory (DFT) calculations to examine the atomic and electronic structure origins of the cathode degradation mechanisms. [1,2]
[1] Adv. Ene. Mater. (Jan. 10, 2019); [2] Adv. Ene. Mater. (Dec. 10, 2024)
