Decoupling Anodic Passivation from Electrodeposition: Synergistic Crystallographic and Electronic Modulation for Energy-Efficient EMD Electrowinning

Abstract

Scalable and energy-efficient manufacturing of electrolytic manganese dioxide (EMD) is critical for the booming alkaline and Li-ion battery markets. However, the process is severely hindered by the intrinsic passivation of titanium anodes in harsh acidic electrolytes. To address this, this study proposes a strategy of active crystallographic symmetry engineering, implemented by fabricating a high-density Ti-20wt%Mn (T20M) solid-solution anode via a tailored powder metallurgy route. By benchmarking against pure Ti, we systematically decouple the correlation between anode surface states and EMD deposition behavior, focusing on the regulatory mechanisms of crystal structure and crystallographic orientation on interfacial oxide growth and EMD nucleation. Results demonstrate that Ti-Mn alloying induces a phase transformation from strongly anisotropic α-Ti (HCP) to highly symmetric β-Ti (BCC) and promotes the formation of a Mn-containing TiOy film during electrolysis, thereby significantly mitigating passivation. In contrast to the anisotropic HCP counterpart, the BCC structure facilitates the growth of a uniform, conductive oxide film and homogeneous current distribution. Multi-scale characterization reveals that this symmetry-driven regulation fundamentally shifts the dynamic competition between anode passivation and EMD deposition. By minimizing orientation dependence, the T20M anode effectively suppresses the formation of high-resistance localized passive films, thereby achieving a low and stable cell voltage even at a high current density of 140 A·m-2 (approximately 400–500 mV lower than that of pure Ti), and extending the stability limit to an ultra-high current density of 220 A·m-2, which significantly improves energy efficiency. This work not only resolves a critical manufacturing bottleneck but also establishes a universal crystallographic design principle for developing robust electrodes for extreme acidic environments.