Structural Reconstruction Driven by Oxygen Vacancies in Layered Ni‐Rich Cathodes

Abstract

However, the LiNi 1-x-y Co x Mn y O 2 (1 − x − y > 0.9) commercialization is hindered, because it suffers from serious structural instability in the long-term cycling due to the crack formation, structure degradation, and cathode-electrolyte interface film formation. [8][9][10] Notably, both the structure formation during calcination and the structure change during attenuation were directly related to the properties for NCM cathodes. [11,12] Currently, much efforts have been done on the structure evolution in the formation (high-temperature lithiation reaction) and degradation (charging/discharging) of NCM cathodes. For NCM formation, Wang and coworkers revealed that the structure change was actually a topological phase transformation process during the high-temperature lithiation of LiNi 0.77 Co 0.1 Mn 0.13 O 2 and involved multiple phase transformations. [1,[13][14][15] For NCM degradation, the loss of active elements, cation migration, and the lattice stress caused by Li + (de)intercalation led to the destruction of the layered structure and the sharp decay of performance during the charging/discharging. [16][17][18][19][20] Structure reconstruction induced by the migration ofLi, O, and transition metal (TM) ions plays a key role in the performance of Ni-based cathodes, yet their interactions are still poorly understood. This work investigates systematically the structure transformation of the high-temperature lithiation in air and oxygen rich atmosphere, charging process, and long-term storage. Structural and electrochemical characterization of Li-free/Li-containing phases (Ni 0.92 Co 0.04 Mn 0.04 (OH) 2 and Li x Ni 0.92 Co 0.04 Mn 0.04 O y ) and a series of detailed analyses provide an in-depth understanding of the structural reconstruction induced by the interaction of Li, O, and TM ions, i.e., the shift of Li/TM ions in the lattice leads to structural reconstruction via a layered structure with oxygen vacancies.

Topotactic Transformation of Surface Structure Enabling Direct Regeneration of Spent Lithium-Ion Battery Cathodes

“…The typical P3̅ m1 structure is composed of edge-sharing octahedra chains in the ab plane in which all the six TM−OH bonds are equal in length and have a similar layered structure to NCM523 cathode materials. 22,23 Considering this, Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 could be a desirable intermediate for the regeneration of SNCM523. Because the TM layered structure of Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 remains unchanged during mixing and calcination with Li source to form the NCM523 cathode material, the transformation from Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 to NCM523 cathode materials is feasible and can be called topotactic transformation (Figure 1e); SNCM523 after targeted surface phase transition is called HSNCM523, and the final regenerated product is denoted as RHSNCM523.…”

Effective and Low-Cost In Situ Surface Engineering Strategy to Enhance the Interface Stability of an Ultrahigh Ni-Rich NCMA Cathode

“…The crystalline structures of B-NCMA, A2-NCMA, A3-NCMA, and A5-NCMA are analyzed using XRD, and the results are displayed in Figure a. All of the samples exhibit the same diffraction peaks indexed to a hexagonal α-NaFeO 2 structure with the R 3̅ m space group and display highly ordered layered structures due to the obvious splits of the (006)/(102) and (108)/(110) peaks. , It indicates that this in situ coating method has little effect on the crystal structure. As can be observed from a magnified view of peak (003) (Figure b), the (003) peaks of the LiAlO 2 -coated samples shift to a lower 2θ angle compared to B-NCMA.…”

Stabilizing lattice oxygen and interface chemistry of Ni-rich and Co-poor cathodes for high-energy lithium-ion batteries

“…8–10 Nonetheless, the lack of Co brings a higher Li/Ni intermixing, which will result in the inhibition of lithium ions diffusion, and induces an anisotropic stress proliferation, causing intergranular crack and even particle fracture. 11,12 In another aspect, inherent interface chemistry and thermodynamics instability of high nickel materials will cause rapid capacity decay and safety issues. 4,7 In terms of electronic structure, e g and t 2g bands of Ni 3+/4+ are coincided with the 2p bond of O 2− , and thus 2p orbitals of O 2− tend to lose electrons and produce O 2 2− , which will be oxidized to O 2 gas on the surface.…”