The increasing energy requirements to power the modern world has driven active research into more advanced electrochemical energy storage devices (EESD) with both high energy densities and power densities. Wide range of newly discovered materials with promising electrochemical properties has shown great potential for next-generation devices, but their performance is normally associated with contradicting demands of thin electrodes and high mass loading that can be hardly achieved for practical applications. Design of three-dimensional (3D) porous electrodes can increase the mass loading while maintaining the effective charge transport even with thick electrodes, which has proven to be efficient to overcome the limitations. 3D structures have also been demonstrated excellent structural stability to withstand strong strains and stresses generated during charge/discharge cycle. 3D printing, which can fabricate various delicate and complex structural designs, thus offering brand-new opportunities for the rational design and facile construction of next-generation EESDs. The recent developments in 3D printing of next-generation EESDs with high performance are reviewed. Advanced/multiscale electrode structures, such as hierarchically porous structure that can be constructed via high-resolution 3D printing or with post-treatment, are further emphasized. The ability of current 3D printing techniques to fulfill multimaterial printing to fulfill simple packaging will be covered.

As one of the essential components for flexible electronics, flexible electrochemical energy storage (EES) has garnered extensive interests at all levels of materials, devices, and systems. The successful implementation of high-performance flexible EES devices relies on exploring of suitable electrode/electrolyte materials that have both superior electrochemical and mechanical properties. For this function, one-dimensional electrospun nanofibers have emerged as a class of promising building blocks for the key components of flexible EES devices. In this overview, the fundamental principles and technical advances of electrospinning are examined, for both their successes and challenges in controllable fabrication of nanofibers with the desirable chemical compositions, micro/meso-/nanostructures, and therefore resultant properties. The advances in applications of electrospun nanofibers for various key flexible EES devices are critically looked into, including those in supercapacitors, metal-ion batteries, and metal-air batteries. The existing challenges and prospects of these electrospun nanofiber-based flexible EES are discussed, aiming to inspire continued efforts in developing the optimal high-performance and low cost flexible EES devices for long-awaited practical applications.