微 型 超 级 电 容 器 的 激 光 加 工 研 究 进 展(特 邀)

Significance Supercapacitors are a new type of energy-storage device that offer advantages such as high capacitance, high instantaneous power density, and long cycle life. Owing to their miniaturization and high integration levels, microsupercapacitors are applied widely in microelectronics, flexible electronics, and mobile devices. Several technologies have been adopted to fabricate microsupercapacitors, among which laser processing has received significant attention because of its unique characteristics. Laser processing is a noncontact method that effectively avoids the destruction of micro-nanostructures in the electrode material, thus sustaining the performance of the electrode material. Additionally, laser processing can regulate the material structure through laserinduced heat, force, and other effects, thus enhancing the activity of the electrode material. It offers a high degree of flexibility and material adaptability, thus rendering it suitable for fabricating supercapacitors with various structures and material characteristics. Laser processing does not require a specific environment; it can achieve high-quality processing under room temperature, normal pressure, and atmospheric conditions. Additionally, laser processing offers a high degree of automation and reproducibility and can satisfy the requirements of mass processing. Hence, it is widely applicable to supercapacitor fabrication. At the forefront of laser-processing technology, ultrafast-laser processing can reduce the size of supercapacitors to the micro-nano scale and alter the properties of microelectrodes, thus further improving the electrochemical performance and integration capability of microsupercapacitors. However, interactions between laser and materials are extremely complicated, thus rendering it challenging to regulate the performance of supercapacitors via laser processing. To date, many laser-processing methods have been developed to fabricate microsupercapacitors on various materials. The effectiveness of ultrafast lasers has been demonstrated in various scenarios. Therefore, it is necessary to summarize the research progress in the laser fabrication of micro supercapacitors and to forecast the future of this field, thus driving continued advancements Progress Supercapacitors exhibit outstanding energy-storage capability and unique operating mechanisms, including electrical double-layer capacitance and pseudocapacitance. Lasers have been widely used to fabricate supercapacitors. Several methods for fabricating supercapacitors using lasers exist, among which three types are discussed herein: laser ablation, laser-induced carbonization, and laser preparation of composite materials. For electrode materials with high conductivity, such as graphene and MoS₂, lasers can be used for material removal to fabricate microelectrodes. This method offers high precision and flexibility as the size and gap width of electrodes can be regulated as necessary. Laser-induced carbonization of polymer and other carbon precursors is the second most widely adopted method for fabricating supercapacitors. In this method, the carbonized area exhibits a porous surface morphology, which is beneficial to the capacitance. Multiple active materials are coated on the carbon precursor and heated by laser simultaneously. Laser-induced carbonization and other laser-synthesis chemical reactions occur simultaneously, thus resulting in composite materials that are suitable for fabricating hybrid supercapacitors. The diverse processing effects of laser facilitate the preparation of other functional materials used in supercapacitors. Ultrafast lasers offer new alternatives in the fabrication of microsupercapacitors. Their processing precision is high owing to their nonlinear absorption and nonthermal ablation effects, which can realize microsupercapacitors with microscale electrode gap widths. By adopting the proposed ultrafast-laser Bessel beam processing method, the electrode gap width can be reduced to 500 nm. The area capacitance of the supercapacitor with nanoelectrode gaps is improved by 2.3 times. Additionally, the ultrafast-laser Bessel beam processing method facilitates the fabrication of large-area device arrays. Ultrafast lasers have higher power densities than continuous lasers; therefore, they can be used to carbonize more types of materials, such as leaves and papers. Ultrafast-laser carbonization is versatile as it can be combined with other technologies such as chemical activation. A new ultrafast-laser-induced in-situ carbonization method was proposed to fabricate microsupercapacitors of various sizes. This method utilizes the carbonized area to absorb laser energy and transfer heat to the unprocessed area, thus controlling the laser energy input and reducing the carbonization linewidth. The linewidth of the carbonized electrode is reduced to less than 10 μm. Ultrafast-laser processing can facilitate the preparation of composite materials, thus offering new methods for fabricating hybrid supercapacitors. A new MoCl₅-assisted ultrafast-laser processing method was proposed. MoCl₅ can assist PI films in absorbing laser energy and generates MoO₃ during laser processing. Porous C/MoO₃ materials are created during laser processing. Microsupercapacitors based on this composite material exhibit improved electrical double-layer capacitance and pseudocapacitance. Conclusions and Prospects This paper reviews methods for fabricating microsupercapacitors, introduces the progress in the ultrafast-laser fabrication of microsupercapacitors, and presents the application potential of laser in this field. In the future, some aspects must be further investigated. First, the laser-processing efficiency must be improved as the electrode requires point-by-point processing with the laser focus. To improve efficiency, laser parallel processing and laser-beam shaping can be adopted. Second, the laser is only used for fabricating microelectrodes in supercapacitors currently. Other procedures are required for the fabrication of electrolytes, which renders the process more complicated and less controllable. New methods should be developed to realize the alloptical fabrication of microsupercapacitors. Third, the capacitance and energy density of microsupercapacitors is limited because of the reduced electrode area. Developing microsupercapacitors with more complex electrode shapes and composited materials will further improve the overall performance of microsupercapacitors. Additionally, the interaction mechanism between laser and capacitor materials must be investigated comprehensively and new methods should be developed for the fabrication of microsupercapacitors to promote the development and application of microsupercapacitors.