Water adsorption and storage characteristics of optimized LiCoO2 and LiNi1/3Co1/3Mn1/3O2 composite cathode material for Li-ion cells

Abstract

This study investigated water adsorption and storage characterization of optimized LiCo O2 and Li Ni13 Co13 Mn13 O2 composite with a weight ratio of 4:1 (LiCo O2: Li Ni13 Co13 Mn13 O2) in terms of the electrochemical properties and metal dissolution upon storage in air or in an electrolyte at 90°C. LiCo O2 and Li Ni13 Co13 Mn13 O2 exhibited moisture (LiOH) and carbon (Li2 C O3) contents of 198 and 627 ppm, respectively, after 7 days storage in air with a relative humidity of 60%. However, the composite sample annealed at 900°C showed moisture content of 100 ppm under the same condition. The simple mixing of LiCo O2 and Li Ni13 Co13 Mn13 O2 exhibited a twofold higher moisture and carbon content than the same material annealed at 900°C. This enhancement was attributed to the possible formation of a structurally robust phase after annealing. The annealed sample showed no reduction in its initial capacity and capacity retention even after exposure to air, compared with the samples before being exposure to air. The results indicate that LiOH and Li2 C O3 at amounts <100 ppm had little influence on the electrochemical properties. Upon 90°C storage at 4.3 V, the concentration of Ni and Co in the electrolyte dissolved from the individual LiCo O2 and Li Ni13 Co13 Mn13 O2 cathodes was >300 ppm but that from the annealed composite was only 70 ppm. Such metals dissolution resulted in local destruction of the LiCo O2 and Li Ni13 Co13 Mn13 O2 structure, but the composite annealed at 900°C for 2 h was structurally stable.