Could Li/Ni Disorder be Utilized Positively? Combined Experimental and Computational Investigation on Pillar Effect of Ni at Li Sites on LiCoO2 at High Voltages

LiCoO2 is a commercial cathode material for Li ion batteries; however, due to the structural instability with more Li+ deintercalation, only half of Li ions in LiCoO2 can be utilized in practical batteries. Therefore, there is still considerable room to improve its capacity if the stability of deliathiated layered structure is enhanced. In this work, we stabilize the delithiated structure by utilizing Li/Ni disorder to introduce Ni into Li layer. Our results demonstrate that, when charged to 4.5V (vs. Li/Li+) at 1 C, the capacity retention of Ni-containing LiCoO2 after 100 cycles is twice that of pristine LiCoO2. In addition, density functional theory computations and ab initio molecular dynamics simulations reveal that Ni in Li layer is immobile in the lattice, and acts as pillars to support the layered structure. Furthermore, the computed diffusion coefficient of Ni-pillared LiCoO2 at 300K is comparable to that of pristine LiCoO2, indicating that a small amount of Ni in the Li layer do not severely block Li diffusion. The pillar effect of Ni in Li layer is confirmed both experimentally and computationally, and the strategy can be generalized to the improvement and design of layered materials for high-voltage Li ion batteries. (C) 2014 Elsevier Ltd. All rights reserved.