Comprehensive evaluation of cobalt-free, high-nickel layered oxide cathodes for lithium-ion batteries

Abstract

Since the advent of layered oxide cathodes that sparked the digital revolution in the 21st century, high-nickel layered oxides LiNiₓM₁₋ₓO₂ (M = Co, Mn, and Al; x > 0.7) have emerged as the leading cathode materials for lithium-ion batteries (LIBs) in electric vehicle (EV) applications, becoming a crucial component in the fight against global warming. However, cobalt usage is problematic from a cost and sustainability perspective due to price volatility from supply shortages, geopolitical instabilities, and sustainability concerns of cobalt mining. Our group has demonstrated the feasibility of completely removing cobalt from high-nickel LiNi₀.₉Mn₀.₀₅Al₀.₀₅O₂ cathode with comparable battery performance, creating an entirely new class of cathode materials like high-nickel LiNiₓMnᵧCo [subscript z] O₂ (NMC) and LiNiₓCoᵧAl [subscript z] O₂ (NCA). To further its path toward practical application, this dissertation unveils the relationship among composition, synthesis conditions, structure, and electrochemical performance of LiNiₓMnᵧAl [subscript z] O₂ (NMA). The capacity fading mechanism of LiNi₀.₉Mn₀.₀₅Al₀.₀₅O₂ in pouch full cell is first elucidated with a combination of electrochemical, structural, and surface analyses. This cathode possesses robust durability and underscores the synergistic benefit of Mn – Al codoping. The impact of cation (Li/Ni) mixing on the cycling stability of LiNi₀.₉Mn₀.₁O₂ is revealed by systematically varying the calcination conditions. An extensive suite of chemical and structural characterization methods discovers a nuanced finding on the consequence of Li/Ni mixing degree that contrasts with popular belief. The nuance of Al³⁺ coprecipitation and its influence on the cycling stability of a series LiNi₀.₉Mn₁₋ₓAlₓO₂ is uncovered by correlating the effect of coprecipitation conditions on the physical and electrochemical properties. The intricate interplay among reaction pH, ammonia concentration, cationic arrangement, and the cycling stability of the calcined cathodes is discussed. Single crystal morphology is employed on Co-free LiNi₀.₈Mn₀.₂O₂ cathode to further improve cycling stability. While it outperforms LiNi₀.₈Co₀.₂O₂ in conventional LIBs, its implementation in all-solid-state batteries (ASSBs) is not as straightforward. A connection between cathode composition, properties, and lithiation behavior in solid-state cathode composite is unveiled. Reducing nickel content in Co-free cathodes can further reduce battery costs. The limit of Ni reduction is demonstrated by comparing the critical performance metrics of Cofree cathodes with decreasing Ni content. An alternative route to reduce Ni content further by blending high-Ni, Co-free layered oxides with olivine LiFePO₄ or LiMn₀.₅Fe₀.₅PO₄ is presented and compared concurrently.