High-nickel layered oxide cathodes for high-performance lithium-ion batteries




Xie, Qiang, Ph. D.

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The ever-growing market of consumer electronics has been driving surging demand for higher-energy-density lithium-ion batteries (LIBs). Since cathode materials primarily dictate the energy density and cost, extensive investigations have been devoted to exploring advanced cathodes for high-performance LIBs. High-nickel layered oxides LiNi [subscript x] M [subscript 1-x] O₂ (x ≥ 0.6, M = Co, Mn, etc.) are one of the most promising candidates and are being extensively pursued. Unfortunately, the practical applicability of high-Ni cathodes is seriously hampered by their poor cyclability, alarming susceptibility to thermal abuse, and decreased air-stability. This dissertation focuses on enhancing the stability of high-Ni cathodes with diverse strategies and advancing the scientific comprehension of high-Ni cathode materials. First, the effect of pillaring Mg-ion doping in the high-Ni cathode LiNi₀.₉₄Co₀.₀₆O₂ is investigated. The incorporation of Mg greatly suppresses the anisotropic lattice collapse and maintains the integrity of cathode particles upon high-voltage cycling, significantly enhancing the cyclability. More importantly, the thermal stability of high-Ni cathodes is notably improved by Mg doping. Second, boron-based polyanion is employed to tune high-Ni cathodes. The introduction of boron-based polyanion enables a well-passivated boron/phosphorus-rich cathode-electrolyte interphase, which alleviates electrolyte corrosion on high-Ni cathodes and thus improves the cyclability. Meanwhile, the boron-based polyanion improves the air stability of high-Ni cathodes as well. Third, a well-designed phosphoric acid treatment approach is presented to modify the high-Ni cathode LiNi₀.₉₄Co₀.₀₆O₂. The implemented treatment not only reduces the detrimental surface residual lithium, but also remarkably improves the electrochemical performance and long-term air-storage stability. Via a range of advanced analytical techniques, the underlying mechanisms involved on the improved performance are disclosed from interphasial and structural perspectives at the nanoscale. Finally, a comparative study is performed to unveil the stabilities of LiNi [subscript 1-x-y] Mn [subscript x] Co [subscript y] O₂ (NMC) cathodes with different Ni contents at identical degrees of delithiation. The overall stabilities of two representative cathodes, LiNi₀.₈Mn₀.₁Co₀.₁O₂ and LiNiO₂, are evaluated with a rigorous control of an identical 70 mol % delithiation. The results suggest that NMC cathodes with higher-Ni contents may have better overall stability than low-Ni NMC cathodes at a given degree of delithiation, disparate from the prevailing belief that high-Ni cathodes with higher-Ni content have inherently reduced stabilities


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