Charge-Transfer-Induced Lattice Collapse in Ni-Rich NCM Cathode Materials during Delithiation

Abstract

Ni-rich LiNi x Co y Mn z O2 (NCM) cathode materials have great potential for application in next-generation lithium-ion batteries owing to their high specific capacity. However, they are subjected to severe structural changes upon (de)­lithiation, which adversely affects the cycling stability. Herein, we investigate changes in crystal and electronic structure of NCM811 (80% Ni) at high states of charge by a combination of operando X-ray diffraction (XRD), operando hard X-ray absorption spectroscopy (hXAS), ex situ soft X-ray absorption spectroscopy (sXAS), and density functional theory (DFT) calculations and correlate the results with data from galvanostatic cycling in coin cells. XRD reveals a large decrease in unit cell volume from 101.38(1) to 94.26(2) Å3 due to collapse of the interlayer spacing when x(Li) < 0.5 (decrease in c-axis from 14.469(1) Å at x(Li) = 0.6 to 13.732(2) Å at x(Li) = 0.25). hXAS shows that the shrinkage of the transition metal–oxygen layer mainly originates from nickel oxidation. sXAS, together with DFT-based Bader charge analysis, indicates that the shrinkage of the interlayer, which is occupied by lithium, is induced by charge transfer between O 2p and partially filled Ni eg orbitals (resulting in decrease of oxygen–oxygen repulsion). Overall, the results demonstrate that high-voltage operation of NCM811 cathodes is inevitably accompanied by charge-transfer-induced lattice collapse.

Chemical, Structural, and Electronic Aspects of Formation and Degradation Behavior on Different Length Scales of Ni‐Rich NCM and Li‐Rich HE‐NCM Cathode Materials in Li‐Ion Batteries

“…The a lattice parameter is assumed to reflect the TM-TM distance (within the TM layer). [62] Hence, the results provide an explanation for the charge-induced shrinkage of the TM-oxygen layer, as seen by operando XRD for NCM811 ( Figure 3a). The c lattice parameter is closely linked to the interslab distance of the Li layers.…”

“…In Li x NiO 2 , the different phase regions can be clearly observed in the voltage profile. [28,[61][62][63]130,[143][144][145][146][147] Comparison of the differential capacity (dQ/dU) with differentials of the c lattice parameter [dc/dU and dc/dx (Li)] and unit cell volume revealed clear correlations, thus providing evidence of the existence of the H2-H3 transformation in the case of LiNi 0.8 Co 0.1 Mn 0.1 O 2 [61,62] and LiNi 0.85 Co 0.1 Mn 0.05 O 2 , [61] in agreement with observations on both LiNi 0.9 Co 0.05 Mn 0.05 O 2 and LiNi 0.95 Co 0.025 Mn 0.025 O 2 by Ryu et al [144] They detected a peak broadening of the 003 reflection, which was ascribed to the coexistence of both phases at the end of charge. [61] However, the voltage curves of high-Ni (≥80%) NCMs reveal an additional plateau at around 4.15 V (vs Li + / Li).…”

“…For reaching the ambitious goals in the electric vehicle and largescale energy storage sectors, sustainable and environmentally friendly solutions providing higher energy density and lower impedance rise in cells using Ni-rich NCM [28,29,[54][55][56][57][58][59][60][61][62][63] and Li-rich HE-NCM CAMs. For reaching the ambitious goals in the electric vehicle and largescale energy storage sectors, sustainable and environmentally friendly solutions providing higher energy density and lower impedance rise in cells using Ni-rich NCM [28,29,[54][55][56][57][58][59][60][61][62][63] and Li-rich HE-NCM CAMs.…”

Phase Transformation Behavior and Stability of LiNiO2 Cathode Material for Li‐Ion Batteries Obtained from In Situ Gas Analysis and Operando X‐Ray Diffraction

“…[48] The H3 phase is detected for the first time when x(Li) = 0.26. [48] The H3 phase is detected for the first time when x(Li) = 0.26.…”

Amorphous Ni‐Rich Li(Ni1−x−yMnxCoy)O2–Li2SO4 Positive Electrode Materials for Bulk‐Type All‐Oxide Solid‐State Batteries

“…As expected, the capacity increased with the Ni content in the NMC active material ( Figure 4b). [40] When all of the lithium ions in NMC are extracted from 80NMC811·20Li 2 SO 4 during the charging state, the theoretical capacity is 215 mAh g −1 . In the XRD pattern, the crystallinity of 80LiNiO 2 ·20Li 2 SO 4 was slightly higher than those of the other structures, indicating that the volumetric fraction of the amorphous matrix was lower than that of the other compositions (Figure 1a).…”