2022 CAP Congress / Congrès de l'ACP 2022

(I) The asymmetric charge-discharge kinetics in Li1−xNi1+xO2 from first principles

9 Jun 2022, 09:15

30m

MDCL 1010 (McMaster University)

Invited Speaker / Conférencier(ère) invité(e) Condensed Matter and Materials Physics / Physique de la matière condensée et matériaux (DCMMP-DPMCM) R1-7 Materials for Energy Applications (DCMMP) | Matériaux pour applications en énergie (DPMCM)

Speaker

Prof. Penghao Xiao (Dalhousie University)

Description

The ever-increasing demand on Li-ion batteries requires the cathode materials to be inexpensive and environmentally friendly. LiNiO${}_2$ is such a promising Co-free cathode. However, the presence of Ni in the Li layer (Ni${}_{Li}$) becomes more common without Co, which limits its electrochemical performance. These excess Ni could randomly distribute in the bulk due to Li deficiency during synthesis, or/and form a surface densified phase due to oxygen loss during cycling. Their interactions with Li, on top of Li-Li interactions, further complicate the non-dilute Li diffusion. In this talk, I will combine the density functional theory (DFT), cluster expansion and kinetic Monte Carlo (KMC) simulations to identify the effects of Ni${}_{Li}$ on Li transport in realistic conditions. Interestingly, both types of Ni${}_{Li}$ impede Li transport at the end of charge and discharge, but not at the beginning. This asymmetry kinetics cannot be solely explained by the Li diffusivity as a function of Li contents but stems from the phase boundary orientation between Li orderings. Ni${}_{Li}$ from synthesis smooths the voltage plateaus and contributes to the 1${}^{st}$ cycle capacity loss. Ni${}_{Li}$ from degradation hinders Li transport more severely when the densified phase fully covers the particle surface. Moreover, this surface phase kinetically traps the last 25% Li for an extremely long time during charge but shows little impedance when Li%>25%. These understandings could open new ways to engineer the transport properties of LiNiO${}_2$-based materials.