Titanium dioxide (TiO₂) is a non-toxic, stable, naturally abundant, and easily synthesized material that has been extensively investigated in various energy fields, including rechargeable ion batteries, solar cells and photocatalysis. Recently, TiO₂ has garnered significant attention as a promising negative electrode material for sodium-ion batteries. However, the ion storage mechanism of TiO₂ remains poorly understood, with existing studies often presenting inconsistent or contradictory results. This review critically summarizes recent researches on advances in understanding the ion storage mechanisms of TiO₂ electrode materials in both lithium-ion and sodium-ion batteries, with a particular focus on the latest findings related to in-situ electrochemically induced crystalline-to-amorphous-to-rock-salt phase transformations. This emerging concept challenges the traditional perspective that irreversible phase evolution is inherently detrimental. Instead, the in-situ formation of new rock-salt phases with enhanced electrochemical storage capabilities for Li⁺ or Na⁺ offers a promising alternative strategy for the design of next-generation TiO₂–based negative electrodes. Furthermore, we highlight a rich yet underexplored research area with significant potential to deepen the understanding of electrochemical phase transitions in TiO₂ and other metal oxide electrodes within energy storage systems.

Three-dimensional (3D) printing, an additive manufacturing technique, is widely employed for the fabrication of various electrochemical energy storage devices (EESDs), such as batteries and supercapacitors, ranging from nanoscale to macroscale. This technique offers excellent manufacturing flexibility, geometric designability, cost-effectiveness, and eco-friendliness. Recent studies have focused on the utilization of 3D-printed critical materials for EESDs, which have demonstrated remarkable electrochemical performances, including high energy densities and rate capabilities, attributed to improved ion/electron transport abilities and fast kinetics. However, there is a lack of comprehensive reviews summarizing and discussing the recent advancements in the structural design and application of 3D-printed critical materials for EESDs, particularly rechargeable batteries. In this review, we primarily concentrate on the current progress in 3D printing (3DP) critical materials for emerging batteries. We commence by outlining the key characteristics of major 3DP methods employed for fabricating EESDs, encompassing design principles, materials selection, and optimization strategies. Subsequently, we summarize the recent advancements in 3D-printed critical materials (anode, cathode, electrolyte, separator, and current collector) for secondary batteries, including conventional Li-ion (LIBs), Na-ion (SIBs), K-ion (KIBs) batteries, as well as Li/Na/K/Zn metal batteries, Zn-air batteries, and Ni–Fe batteries. Within these sections, we discuss the 3DP precursor, design principles of 3D structures, and working mechanisms of the electrodes. Finally, we address the major challenges and potential applications in the development of 3D-printed critical materials for rechargeable batteries.