IntroductionA high-nickel ternary cathode material of LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) has a high energy density. However, this material suffers from interfacial/structural instability, leading to a loss of more than 10% of its capacity during cycling. Cathode materials can be surface coated to improve their overall performance, in which nano-powder of zirconium dioxide can be used as a coating material to effectively improve the structural stability of high nickel ternary materials. However, the method for zirconia preparation has some disadvantages like complicated process flow, high production cost, and easy particle agglomeration. Flame spray pyrolysis (FSP) is simple in operation, fast in reaction speed, high in product quality, and easy to scale up production. In this paper, a variety of metal-based nanomaterials with small particle sizes and well-dispersity were prepared via FSP. The effect of process parameters (i.e., precursor solution concentration, feed rate and hydrogen flow rate) on the particle size, morphology and specific surface area of the powder was investigated. The synthesis process parameters of ZrO₂ were optimized, and the effect of optimal parameters on the coating modification of high-nickel ternary cathode materials was analyzed.MethodsA certain amount of ZrCl₄ was weighed and dissolved in ethanol, and stirred at 40 ℃ to dissolve it completely and formulate precursor solutions at different concentrations (i.e., 0.16, 0.50, and 1.00 mol/L). At different hydrogen flow rates (3.3, 6.6, and 9.9 L/min) and feed rates (3, 5, and 7 mL/min), the precursor solutions with different concentrations were injected into a flame spray pyrolysis unit by a syringe pump. Finally, ZrO₂ powder was collected through a filter. The physical and chemical properties of the powders were determined by Brunauer-Emmett-Teller (BET) surface area analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD), and laser particle size (DLS) analysis.Results and discussionThe specific surface area of ZrO₂ is inversely proportional to the feed rate, and the particle size of ZrO₂ is directly proportional to the feed rate. The specific surface area of ZrO₂ powder decreases from 54.89 m²/g to 28.99 m²/g as the feed rate of precursor increases from 3 mL/min to 7 mL/min. Also, the distribution of particle size gradually becomes wider, and the average particle size obtained from the fitting increases from 7 nm to 18 nm. The specific surface area of ZrO₂ is inversely proportional to the hydrogen flow rate, and the particle size of ZrO₂ is directly proportional to the hydrogen flow rate. The uniformity of the particle size distribution of ZrO₂ nanoparticles decreases, and the fitted average particle size gradually increases from 7 nm to 10 nm, while the specific surface area of the product decreases from 61.57 m²/g to 44.73 m²/g as the hydrogen flow rate increases from 3.3 L/min to 9.9 L/min.The specific surface area of ZrO₂ is inversely proportional to the precursor concentration, and the particle size of ZrO₂ is proportional to the precursor concentration. The specific surface area of ZrO₂ gradually decreases from 71.58 m²/g to 45.29 m²/g, the particle size gradually increases from 6 nm to 11 nm, meanwhile, and the large-size particles increases significantly as the precursor concentration increases from 0.16 mol/L to 1.00 mol/L.ConclusionsZirconium dioxide nanoparticles with a high specific surface area, a small particle size and a good dispersibility could be prepared via flame spray pyrolysis with ZrCl₄ as a precursor, ethanol as a solvent at a feed rate of 3 mL/min, a hydrogen flow rate of 3.3 L/min, and the concentration of precursor solution of 0.16 mol/L. The feed rate, hydrogen flow rate and precursor concentration all affected the particle size and specific surface area of the product, and the effect of the feed rate was dominant. A lower feed rate was favorable for the synthesis of ZrO₂ particles with a smaller particle size and a larger specific surface area. A high hydrogen flow rate exacerbated the agglomeration of ZrO₂ particles and reduced their specific surface area. A high concentration of precursor solution induced the generation of more large-sized particles, resulting in a decrease in the specific surface area. Zirconia obtained under the optimal process conditions of 0.2% (mass fraction) coating on the surface of NCM811 cathode material could increase the capacity retention of the battery by 14% at 1 C and 2.7-4.3 V. Nano-sized powder of zirconium dioxide was prepared via flame spray pyrolysis at suitable process parameters, providing a promising method for the preparation of zirconium dioxide powder with a small particle size and a high specific surface. In addition, the application in anode capping could also improve the comprehensive performance of the battery.