<p>Yolk–shell structures, defined by their core@void@shell architecture, have garnered considerable interest due to their tunable physical and chemical properties, which make them suitable for applications in nanoreactors, drug delivery, energy storage, biosensing, and surface-enhanced Raman scattering. However, conventional synthesis techniques, such as templating and non-templating liquid-phase methods, are often labor-intensive, time-consuming, and challenging to scale. Recently, spray pyrolysis has gained attention as a rapid, one-pot, and continuous synthesis method offering high scalability and production efficiency. This study presents a novel strategy for synthesizing uniform yolk–shell microspheres via spray pyrolysis, augmented by in situ polymerization and the addition of a drying control agent. By systematically varying carbon sources, including citric acid, ethylene glycol, sucrose, and polyvinylpyrrolidone, their influence on particle size distribution and yolk–shell formation were investigated. A novel formation mechanism involving metal–metal oxide–carbon intermediates was proposed to explain the observed morphologies. This approach led to enhanced spherical uniformity and structural consistency, supported by the use of drying control agents. As a case study, nickel oxide yolk–shell particles were synthesized and subsequently converted into nickel sulfide@C microspheres, which exhibited promising performances as anode materials in potassium-ion batteries. Overall, this method provides a scalable, efficient, and versatile route for fabricating yolk–shell structures with customizable features for advanced technological applications.</p> Graphical abstract <p></p>