Ultrasonic Spray Deposition as a Superior Strategy for Electrochemically Stable and Scalable Battery Electrodes in Structural Batteries

The electrochemical performance and durability of lithium-ion battery electrodes are strongly influenced by coating uniformity, interfacial contact, and microstructural stability. These challenges are amplified when transitioning from conventional planar current collectors to complex, multifunctional architectures such as carbon fiber reinforcements used in structural batteries. Traditional coating approaches such as dip coating, electrophoretic deposition, and manual spray techniques often result in nonuniform coatings, particle agglomeration, and inconsistent electrochemical utilization, limiting cycle life, reproducibility, and scalability. This study aims to demonstrate that ultrasonic spray deposition is an effective and enabling coating strategy for fabricating composite electrodes on carbon fiber substrates. LiFePO₄ (LFP)-coated carbon fiber cathodes are employed as a model system to evaluate the influence of ultrasonic atomization on coating morphology and electrochemical behavior. The ultrasonic process generates fine, deagglomerated droplets that form continuous, conformal coatings with controlled thickness and uniform particle distribution along individual fibers, maximizing electrochemically active surface area while maintaining intimate contact with the conductive carbon network. Electrochemical characterization in Li/Li⁺ half-cells reveals well-defined and highly reversible LFP redox behavior, stable two-phase lithiation/delithiation plateaus, and near-unity coulombic efficiency over extended cycling. At a moderate rate of 0.5 C, ultrasonic-coated carbon fiber electrodes deliver approximately 100 mAh g⁻¹ of LFP and retain more than 80% of their initial capacity after 350 cycles. This cycling stability significantly exceeds values commonly reported for electrodes fabricated using conventional coating methods for structural batteries. The enhanced electrochemical performance is attributed to homogeneous current distribution, improved electrode-electrolyte contact, and reduced microstructural degradation enabled by the uniformity and conformality of ultrasonic deposition. Beyond electrochemical performance, ultrasonic spray coating offers key manufacturing advantages, including precise control over coating parameters, high reproducibility through computer-controlled deposition, compatibility with complex geometries, and minimal material waste. These attributes position ultrasonic coating as a scalable and versatile manufacturing approach for multifunctional energy storage systems. Overall, this study establishes ultrasonic spray deposition not merely as an alternative coating method, but as a leading platform technology for the fabrication of composite electrodes in structural batteries. The combination of electrochemical stability, architectural adaptability, and manufacturing consistency makes ultrasonic coating particularly well suited for next-generation energy storage systems that integrate mechanical load-bearing and electrochemical functionality.