Cobalt suppressed Jahn–Teller effect in LiCo0.5Ni0.5O2 for lithium ion batteries

The structural and electronic properties of LiCo0.5Ni0.5O2 are studied from first principles calculations. Results show that Ni3+ ions in LiNiO2 have the (t2g)6(dz2)1 electronic configuration, which gives rise to obvious Jahn–Teller (JT) distortion to the NiO6 octahedral in the lattice. In LiCo0.5Ni0.5O2 however, Ni ions exhibit a (t2g)6(eg)2 electronic configuration that is no longer JT active. Co ions suppress JT distortion of NiO6 in LiCo0.5Ni0.5O2 through charge transfer from Co-3d orbital to nearby Ni-3d orbital. As a result the t2g orbital of Co-3d becomes partly empty, which makes the LiCo0.5Ni0.5O2 compound metallic and has better electrical conductivity than both LiCoO2 and LiNiO2.

Research highlights
► The Jahn–Teller distortion of NiO6 in LiNiO2 is clearly reproduced from DFT+U calculations.
► The physical picture of the Co suppressed JT effect in LiCo0.5Ni0.5O2 is clearly demonstrated.
► Charge transfer to Ni is the main reason that accounts for the suppressed JT distortion.