Quantifying the thermochemical stability of high-nickel LiNi_0.9Mn_0.05Co_0.05O₂: Single-crystalline vs. polycrystalline

As nickel content of LiNi_xMn_yCo_1-x-yO₂ material increases, the thermochemical stability decreases. The crystal structure is one of the key factors influencing thermochemical stability. Herein, the difference in thermochemical stability between single-crystalline and polycrystalline LiNi_0.9Mn_0.05Co_0.05O₂ is quantified by gas evolution and surface species distribution at temperature ranging from room temperature to 100 °C. C₂H₆ and CH₄ emission is suppressed by 69 % and 52 % in single-crystalline NMC, showing better thermochemical stability than polycrystalline NMC. Formation of thermally stable inorganic species is promoted on the surface of single-crystalline NMC electrode. Relationship of gas evolution and surface species distribution is revealed, a monotonic increase of 20.3 % in stable inorganic composition of cathode electrolyte interface on single-crystalline NMC. With the generation of H₂ and CO₂, stable inorganic species like LiF on cathode electrolyte interface and solid electrolyte interface are promoted in single-crystalline NMC while unstable organic species like LiPO_xF_y decomposition is favoured in polycrystalline NMC. This work provides a quantifying method for evaluating thermochemical stability of high nickel content NMC.