Effect of Cationic Uniformity in Precursors on Li/Ni Mixing of Ni-Rich Layered Cathodes

Abstract

Ni-rich layered oxides are promising cathodes to satisfy the long driving range of electric vehicles. However, Li/Ni mixing becomes a critical issue, which affects nearly all of the aspects of electrochemical performance of Ni-rich layered cathodes, such as cycling stability, rate capability, discharge capacity, and thermal stability. Herein, we investigate the effect of cationic uniformity in the precursors on Li/Ni mixing of Ni-rich layered cathodes. The cationic uniformity in precursors is regulated by the sol–gel and solvothermal method. All cations in the precursors obtained by the sol–gel method mix uniformly at a molecular scale, while the solvothermal method with a postaddition of Li salts causes a heterogeneous mixture between Li and transition-metal ions. Refined XRD and TEM results demonstrate that the NCM811 sample synthesized by the solvothermal method shows a higher Li/Ni mixing. This is because the inhomogeneous distribution of cations leads to local Li-poor regions, in which some Ni2+ ions are produced to keep charge neutrality, resulting in a serious Li/Ni mixing. Part of Ni ions in the Li layer suppresses the H2–H3 transition while it delivers a low capacity for increased electrode resistance. Therefore, advanced Ni-rich layered cathodes of the next-generation high-energy Li-ion batteries should simultaneously possess low Li/Ni mixing and reversible H2–H3 transition.

Theoretical Insights into High-Entropy Ni-Rich Layered Oxide Cathodes for Low-Strain Li-Ion Batteries

“…This mixing amount agrees well with the available experimental results (5.85%). 127 From r2SCAN-D3 and PBE+U+D3, we obtained similar trends for E mixing , lending validity to our analysis.…”

Competitive Doping Chemistry for Nickel‐Rich Layered Oxide Cathode Materials

“…After 100 cycles, both NCM and NCM-AB exhibit layered structure as shown in Figure S14, except the smaller ratio of the intensity of (003) to (104) of NCM electrode, namely, the serious Li/Ni exchange. [14] The increased Li/Ni exchange was confirmed by electron energy loss spectra (EELS) collected from the surface to bulk of the cycled NCM and NCM-AB particles. The fine structure and energy position evolution of NiÀ L edges (Figure 4e, f) and the OÀ K edges (Figure S15) was used to investigate the electronic structure changes of the material upon cycling.…”

“…The structural stability engendered by Al and B co‐modification was verified by ex situ SEM (Figure S13): the NCM particles were almost pulverized due to the larger inner stress during cycles, whereas NCM‐AB electrode maintains the good spheroidal structure with few cracks. After 100 cycles, both NCM and NCM‐AB exhibit layered structure as shown in Figure S14, except the smaller ratio of the intensity of (003) to (104) of NCM electrode, namely, the serious Li/Ni exchange [14] …”

Oxygen Anion Redox Chemistry Correlated with Spin State in Ni‐Rich Layered Cathodes

“…Meanwhile, at ≈600 cm −1 , a peak representing a cation antisite defect was distinctly observed in the spectrum of 811‐A but not in that of 811‐D. [ 30 ] In Figure 1f (633 nm), the differences between the two samples shown in Figure 1e are significantly weakened, demonstrating that a large number of aggregated Li/Ni antisite defects appeared on the 811‐A surface but not on the 811‐D surface.…”

“…In Figure 1e (532 nm), compared with 811-L, 811-H exhibits a spectrum with a slight move to a lower Raman shift, which is explained by the lower response wave number for Ni than for Mn (or Co). Meanwhile, at ≈600 cm −1 , a peak representing a cation antisite defect was distinctly observed in the spectrum of 811-A but not in that of 811-D. [30] In Figure 1f (633 nm), the differences between the two samples shown in Figure 1e are significantly weakened, demonstrating that a large number of aggregated Li/Ni antisite defects appeared on the 811-A surface but not on the 811-D surface.…”