Solid-state chemistry and electrochemistry of LiCo1/3Ni1/3Mn1/3O2 for advanced lithium-ion batteries III. Rechargeable capacity and cycleability

Reaction mechanism of LiCo1/3Ni1/3Mn1/3O2 was examined by ex situ X-ray diffraction (XRD) and electrochemical methods. According to XRD results, the change in hexagonal lattice parameters was quite similar to that of Li1-xCo1/2Ni1/2O2, i.e., the unit cell volume was almost constant at 0 <= x < 2/3 in Li1-xCo1/3Ni1/3Mn1/3O2, indicating homogeneous phase reaction over an entire range. Reversible-potential measurements on Li1-xCo1/3Ni1/3Mn1/3O2 (0 <= x < 1) against a lithium electrode were also carried out and the solid-state redox reactions were described by applying the concept of electrochemical density of states (EDS). Gibbs free-energy change for the reaction of Li+square Co1/3Ni1/3Mn1/3O2 -> LiCo1/3Ni1/3Mn1/3O2 was obtained to be Delta G=-398 kJ mol(-1), which was slightly higher than that for LiCo1/2Ni1/2O2 (-393 kJ mol(-1)). Rechargeable capacity (Q) as a function of charge-end voltage (E-ce) was examined for Li/LiCo1/3Ni1/3Mn1/3O2 cells and the relation between Q in mAh g(-1) and E-ce in V was given to be Q=151+121 (E-ce-4.2). From these results, rechargeable capacity and cycleability as a function of charge-end voltage are discussed in relation to the reaction mechanism of LiCo1/3Ni1/3Mn1/3O2.