ADVANCED MATERIALS & PROCESSES | APRIL 2024 25 bed fusion, and traditional vat photopolymerization processes (e.g., stereolithography and digital light processing), and even down to a submicroscopic level for the two-photon polymerization process (i.e., an offshoot of the vat photopolymerization category)[9]. In the context of battery manufacturing, this level of control opens the way toward the development of components with controlled porosity[10], tuned electronic conductivity, as well as improved mechanical and electrochemical performance. Figure 2 illustrates the characteristics of various 3D printing processes and their potential to manufacture batteries. Technical parameters such as printing speed, resolution, ability to build tall 3D structures in the z-axis, machine cost, and multi-material option availability, are considered. As shown in Fig. 2, the perfect additive manufacturing process for 3D printing batteries currently does not exist, because each process has advantages and challenges. A solution that has been proposed in literature[11] consists of combining several processes (also referred to as hybrid additive manufacturing)[12] to print different battery components, thus taking advantage of the full capabilities conferred by each independent AM technology. An overview of current challenges and perspectives related to the 3D printing of batteries is presented in the next section. CHALLENGES AND OUTLOOK While the benefits conferred by additive manufacturing for batteries are undeniable, challenges such as production speed, process scale-up, manufacturing accuracy, shelf life of feedstock materials (e.g., filaments, inks, photocurable resins, and powder), post-processing steps, and the need for multi-material 3D printing systems, still need to be addressed (Fig. 3). While additive manufacturing enables rapid prototyping and iterative design for a wide range of industries such as automotive, aerospace[13], and defense, leading to faster innovation cycles and reduced time-to-market, this unfortunately cannot be applied to the battery field yet. Among the challenges related to the process, production speed is one of the most difficult to overcome. Indeed, most of the 3D printing processes still remain slow (µm/min to cm/min), and achieving consistent quality across an eventual large-scale production remains a challenge in comparison with traditional tape-casting rates (m/min). The printing itself is limited by the manufacturing accuracy of individual machines, which is given by the resolution of the extruder nozzle in fused deposition modeling, the tip of the syringe in direct ink writing, the light in vat photopolymerization, or the physicochemical properties of the powder in powder bed fusion, to mention a few. Clever solutions in the literature combined feedstock materials engineering[14], printing parameters optimization[11], and machine modifications[15] to achieve the maximal printing accuracy. In-situ process monitoring ensuring the quality and reliability of the final battery components is crucial to maintain consistency. A recent article[6] has discussed this topic related to the area of material extrusion, emphasizing that modifications to current 3D printers are needed in order for 3D printed batteries to be widely produced outside niche applications. A challenge that is often disregarded at the laboratory scale is the physicochemical stability of the printable composite material feedstocks loaded with battery materials. Sedimentation issues often arise for inks and resins containing a high loading of active material and conductive additives, thus resulting in printed electrodes with undesirable compositions. Composite filament feedstocks loaded with battery materials are also prone to lose flexibility over time and become more brittle[16]. Some battery materials that are contained in the feedstocks are also highly sensitive to air and/or moisture[17], which ultimately have a detrimental effect on the battery performance (faster capacity fading)[18]. There are several ways to tackle these issues. The first is to incorporate additives that improve shelf-life, such as plasticizers, antioxidants, UV-stabilizers (colorants), oxygen scavengers, and lubricants. Note that these additives are not necessarily compatible with the environment inside a battery, and therefore a careful chemical analysis must be done before using them. Another option is to improve the Fig. 2 — Chart summarizing the advantages and drawbacks of various additive manufacturing processes.
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