An approach to low-temperature flame spray pyrolysis for the synthesis of temperature-sensitive materials: Application to Li1.2Mn0.54Ni0.13Co0.13O2

Abstract

Flame spray pyrolysis (FSP) is a robust, scalable method of synthesizing powders. Nonetheless, many materials cannot be synthesized by FSP because their properties degrade when exposed to the high temperatures typical of flame processes. Herein, a low-temperature flame spray pyrolysis (LT-FSP) process is proposed, and the method is applied to the synthesis of a lithium, manganese rich-NMC material (LMR-NMC): Li1.2Mn0.54Ni0.13Co0.13O2. LMR-NMC materials have been studied intensively in the past decades and are some of the more attractive cathode materials under study for electric vehicles. However, their performance degrades if synthesized under the high temperatures typical of FSP.The proposed LT-FSP process incorporates ethanol, added to an aqueous precursor, as the fuel. Ethanol's unique properties -including a high vapor pressure enhanced by its high activity coefficient in water- allow for stable combustion and low post-flame temperature. Using a swirl-stabilized burner, a stable flame for the mixture was achieved, and the subsequent reactor temperature was found to be significantly lower than what can be attained via traditional FSP. The effects of reactor temperature, controlled via altering ethanol concentration, on the physical properties and electrochemical performance of the synthesized materials were characterized. Li1.2Mn0.54Ni0.13Co0.13O2 synthesized with 25 wt% ethanol showed the best performance, delivering a discharge capacity of 203 mAhg−1 after 100 cycles under C/3, and an initial capacity of 201 and 169 mAhg−1 at C/2 and C/1, respectively. These results are comparable to those obtained for Li1.2Mn0.54Ni0.13Co0.13O2 produced via co-precipitation.The process was modelled via RANS CFD to demonstrate that the high volatility of ethanol in water yields stable combustion at the base of the flame and a uniform low-temperature zone afterwards, leading to ideal conditions for synthesis of temperature sensitive materials in a scalable process. LT-FSP was also found to lead to improved material uniformity when compared to another spray pyrolysis method.