Unraveling the Origin of Instability in Ni-Rich LiNi_1–2xCo_xMn_xO₂ (NCM) Cathode Materials

Abstract

In this work, phase stability of Ni-rich LiNi1–2x­Co x Mn x O2 (NCM) (x < 0.20) is investigated by means of a bond model based on the effective interaction of transition metal (TM) ions (represented as TM–TM bond), fitted to results obtained within the DFT+U framework. The developed bond model reveals the intrinsic relationship between phase stability and TM–TM bonds, which explains the different roles of TM ions in the phase stability of Ni-rich NCM. A sequence of TM–TM bond strengths (Mn4+Mn4+ > Ni2+Mn4+ > Ni3+Mn4+ > Co3+Mn4+ > Co2+Mn4+ > Ni2+Ni4+) is then predicted by bond model and subsequently used to understand the intricate layered LiTMO2 (TM = Ni, Co, Mn) phase triangle. Our results also show that Co and Mn ions segregate to form clusters within the Ni environment when x < 0.1 (Ni ≥ 80 at. %), and such segregation is responsible for the electrochemical degradation during cycling. The obtained results agree excellently with the validation experiment in the present work and also other experiments in the literature, and could help to clarify the existing controversies about the origin of the instability of Ni-rich NCM compounds. Finally, we show that, by tailoring the TM–TM interaction, i.e., the atomic uniformity of the as-synthesized cathode material, the electrochemical stability of the Ni-rich NCM can be substantially improved.

Intrinsic Origins of Crack Generation in Ni-rich LiNi0.8Co0.1Mn0.1O2 Layered Oxide Cathode Material

“…2a–d and 2e–h, respectively). In the fully lithiated state (Li 1 Ni 0.8 Co 0.1 Mn 0.1 O 2 ), the Ni, Co, and Mn d -orbitals are shown as Ni 3 -like, Co 3+ , and Mn 4+ -like shapes due to the effect of the d -electronic donor938, in agreement with a previous report10. The thermodynamic stability of the Co 3+ and Mn 4+ crystal fields could be satisfied by maintaining their separate locations.…”

“…described the surface reconstruction and chemical evolution of the rhombohedral layered structure to a cubic spinel structure using high-throughput X-ray absorption spectroscopy8. As theoretical approaches, electronic correlations for the redox reactions between the multivalent transition metals in the Ni-rich NCM9 and stability analysis with respect to the various ratios of the Ni, Co, and Mn components in the NCM10 have been performed through first-principles calculations. On the bases of these fundamental data, many researchers have suggested solutions to resolve the cyclic degradation problem.…”

Simultaneously Dual Modification of Ni‐Rich Layered Oxide Cathode for High‐Energy Lithium‐Ion Batteries

“…The NCM sample exhibits a broad exothermal peak around 228.58 °C with a heat generation of 1141 J g −1 , while the LT1 sample shifts to a higher temperature (243.97 °C) and overall heat generation was reduced to 655.8 J g −1 . The six oxygen atoms around the substituted Ni and doped Ti are shown in Table S6 (Supporting Information), it clearly shows that the Ti doping share more electrons to the oxygen around, which agrees well with the charge difference analysis in Figure d, suggesting stronger bond strength of Ti–O than that of Ni–O . Owing to the stable structure, the modified sample shows an enhanced thermal stability at elevated temperature.…”

A review on first principles based studies for improvement of cathode material of lithium ion batteries

“…Further study comprising Zr and P coating on LiNiMnO 2 reveals that electrochemical performance has been enhanced due to the synergistic effect of coated materials. An increase in capacity to 209.3 mAh/g as compared with the case without coating of 207.4 mAh/g was found at 1C charge/discharge rate along with an increase in capacity retention, with decrease in Li residual amount in the sample from 3693 ppm to 2525 ppm [67] .…”