Undecomposed LiNO3 enhances Ni-rich cathodes for lithium-ion battery via flame-assisted spray pyrolysis

Flame-assisted spray pyrolysis (FASP) is emerging as a promising approach for synthesizing Ni-rich cathodes of lithium-ion batteries (LIBs). In conventional wet chemistry approaches, lithium nitrate (LiNO 3 ) is frequently utilized as an effective flux to achieve enhanced battery performance; yet LiNO 3 is usually decomposed completely during current FASP that operates under high flame temperatures. Thermogravimetric analysis (TGA) for LiNO 3 and transition metal nitrates (Ni, Co, Mn) reveals that they are actually starting (and finishing) decomposing in much lower temperatures than previous studies assumed. And more importantly, there exists a notable gap of decomposition temperature (up to 356 °C) between LiNO 3 and the transition metal nitrates. Based on these findings, the present study proposed a low-temperature strategy to achieve only partial decomposition of LiNO 3 during FASP and taking advantage of the fluxing function of LiNO 3 to realize improved electrochemical performance of Ni-rich cathodes for LIBs. Specifically, an experimentally and theoretically confirmed low-temperature ∼665 °C of the co-axil flame was designed, which was shown to completely decompose the three transition metal nitrates while only partially decompose LiNO 3 . The undecomposed LiNO 3 was characterized and shown to act as a flux during the subsequent calcination stage, promoting the formation of NCM811 with larger primary particles, improved structural ordering, and reduced Li + /Ni 2+ cation mixing. Consequently, the synthesized Ni-rich cathode material achieved superior cycling stability (86.4% capacity retention after 100 cycles at 0.33 C) and rate performance (136.8 mAh/g at 5 C), notably outperforming the samples by the controlling high-temperature (∼1180 °C) strategy. The findings of the present work offered a new conception for the effective synthesis of high-performance Ni-rich cathodes through flame-assisted spray pyrolysis. Novelty and significance statement The present study introduces a novel low-temperature FASP strategy that selectively retains undecomposed LiNO 3 to utilize its intrinsic fluxing properties. Thermogravimetric analysis identifies a > 350 °C decomposition gap between LiNO 3 and transition-metal nitrates, enabling controlled partial decomposition of LiNO 3 , in contrast to current high-temperature FASP that melts and decomposes all salts indiscriminately. The undecomposed LiNO 3 during synthesis enables the growth of single-crystal-like NCM811 with enhanced structural ordering and reduced cation mixing, leading to superior electrochemical performance, all within a rapid, one-step flame synthesis process. These findings reveal how tailored flame conditions can direct intermediate material evolution, offering the combustion community a new strategy for designing complex functional nanomaterials and advancing the role of flame synthesis in energy applications.