Atomic-Resolution Visualization of Distinctive Chemical Mixing Behavior of Ni, Co, and Mn with Li in Layered Lithium Transition-Metal Oxide Cathode Materials

Abstract

Capacity and voltage fading of layer structured cathode based on lithium transition metal oxide is closely related to the lattice position and migration behavior of the transition metal ions.However, it is scarcely clear about the behavior of each of these transition metal ions in this category of cathode material. We report direct atomic resolution visualization of interatomic layer mixing of transition metal (Ni, Co, Mn) and lithium ions in layer structured oxide cathodes for lithium ion batteries. Using chemical imaging with aberration corrected scanning transmission electron microscope (STEM) and DFT calculations, we discovered that in the layered cathodes, Mn and Co tend to reside almost exclusively at the lattice site of transition metal (TM) layer in the structure or little interlayer mixing with Li. In contrast, Ni shows high degree of interlayer mixing with Li. The fraction of Ni ions reside in the Li layer followed a near linear dependence on total Ni concentration before reaching saturation. The observed distinctively different behavior of Ni with respect to Co and Mn provides new insights on both capacity and voltage fade in this class of cathode materials based on lithium and TM oxides, therefore providing scientific basis for selective tailoring of oxide cathode materials for enhanced performance.

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…Commonly, in the site of TM ions, it can be occupied by a combination of Ni, Co, and Mn as well as some other doping cations, typically Al ions in the case of NCA . Two kinds of Li‐ion diffusion pathways in such O3‐type layered structure have been demonstrated in Figure b, namely, Li ions diffuse from one octahedral site to next site through the oxygen dumbbell or an intermediate tetrahedral site, in which Li ions tend to choose oxygen dumbbell hopping at the early stage of charging (delithiation), and tetrahedral site hopping begins to dominate when more than 1/3 Li ions are extracted . Their effective diffusion barriers depend on activation energies and Li‐slab space (d 2 , d 1 + d 2 = d (001) ) in the Ni‐rich cathodes .…”

Thermally-driven mesopore formation and oxygen release in delithiated NCA cathode particles

“…1 Despite their high capacities of 220 mAh/g and the potential to reach even higher capacities of > 250 mAh/g when cycled to 4.6 V, 2,3 layered Ni-rich oxides still face some major limitations. A significant drawback of high Ni content layered oxides is their intrinsic instability in their delithiated state, which occurs because of the effect of cation mixing: [4][5][6][7][8][9] The similar radii of Li ions (0.76 Å) and Ni 2+ ions (0.69 Å) enable Li + /Ni 2+ site exchange, e.g. the occupation of 3b Li + layer sites by Ni 2+ .…”

Elucidation of the surface characteristics and electrochemistry of high-performance LiNiO2

“…[3][4][5][6] A combination of different transition metals (e.g., LiNi x Mn y Co z O 2 or NMCs) further increases the complexity of the problem since phase separation and side reactions with electrolyte have been reported for different compositions. 7,8 Herein, we report a comprehensive study on the effect of various solid-state synthesis parameters on the crystal structures, morphologies, and surface characteristics of layered lithium nickel oxides and correlate these characteristics with electrochemical performance. The best LiNiO 2 demonstrated excellent electrochemical performance including high discharge capacity, good rate capability, and capacity retention.…”