Origin of oxygen-redox and transition metals dissolution in Ni-rich LixNi0.8Co0.1Mn0.1O2 cathode

Chun Cai; Dantong Zhang; Qi Zhang; Kunfeng Chen; Wenchao Hua; Chao Peng; Dongfeng Xue

doi:10.1063/5.0139471

Origin of oxygen-redox and transition metals dissolution in Ni-rich Li_xNi_0.8Co_0.1Mn_0.1O₂ cathode

J Chem Phys. 2023 Mar 21;158(11):114703. doi: 10.1063/5.0139471.

Authors

Chun Cai¹, Dantong Zhang¹, Qi Zhang¹, Kunfeng Chen², Wenchao Hua³, Chao Peng¹, Dongfeng Xue¹

Affiliations

¹ Multiscale Crystal Materials Research Center, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China.
² State Key Laboratory of Crystal Materials, Institute of Novel Semiconductors, Shandong University, Jinan 250100, China.
³ GEM Super Green Technology Research Institute, Taohuayuan Science and Technology Innovation Park, Shenzhen 518101, China.

PMID: 36948826
DOI: 10.1063/5.0139471

Abstract

Recently, Ni-rich LiNi_xCo_yMn_1-x-yO₂ (x ≥ 0.8) draw significant research attention as cathode materials in lithium-ion batteries due to their superiority in energy density. However, the oxygen release and the transition metals (TMs) dissolution during the (dis)charging process lead to serious safety issues and capacity loss, which highly prevent its application. In this work, we systematically explored the stability of lattice oxygen and TM sites in LiNi_0.8Co_0.1Mn_0.1O₂(NCM811) cathode via investigating various vacancy formations during lithiation/delithiation, and properties such as the number of unpaired spins (NUS), net charges, and d band center were comprehensively studied. In the process of delithiation (x = 1 → 0.75 → 0), the vacancy formation energy of lattice oxygen [E_vac(O)] has been identified to follow the order of E_vac(O-Mn) > E_vac(O-Co) > E_vac(O-Ni), and E_vac(TMs) shows a consistent trend with the sequence of E_vac(Mn) > E_vac(Co) > E_vac(Ni), demonstrating the importance of Mn to stabilize the structural skeleton. Furthermore, the |NUS| and net charge are proved to be good descriptors for measuring E_vac(O/TMs), which show linear correlations with E_vac(O) and E_vac(TMs), respectively. Li vacancy plays a pivotal role on E_vac(O/TMs). E_vac(O/TMs) at x = 0.75 vary extremely between the NiCoMnO layer (NCM layer) and the NiO layer (Ni layer), which correlates well with |NUS| and net charge in the NCM layer but aggregates in a small region in the Ni layer due to the effect of Li vacancies. In general, this work provides an in-depth understanding of the instability of lattice oxygen and transition metal sites on the (104) surface of Ni-rich NCM811, which might give new insights into oxygen release and transition metal dissolution in this system.