Aerogels, additive manufacturing, and energy storage

The global push toward decarbonization and electrification has led to a rapidly growing research effort to achieve ever-increasing device performance goals. These efforts have resulted in novel electrochemical energy storage devices (EESDs) with a variety of chemistries and materials, such as aerogels, which have significantly improved energy densities, power densities, and rate capabilities. To date, using thin-film electrode designs has been the state of the art, but with the need for increased performance, new and innovative approaches are being pursued. One approach to meeting the continued demand to increase performance is to increase the fraction of active materials in the EESD (i.e., eliminating current collector and separator) by moving to thicker electrodes. Thick electrodes enable high-mass loading of active materials, which can effectively boost capacity and energy density. The increased mass loading of active materials also decreases the relative content of inactive components, such as substrates, current collectors, and separators, which helps to save cost, weight, and volume of the device. For devices with restricted footprint areas, such as on-chip power supplies, the application of thick electrodes can fully utilize the empty volume in these devices, which maximizes their energy storage capacity. However, using a thick electrode will require finding novel methods to overcome ion-transport limitations. The distance and resistance of electron/ion transport through the electrode proportionally increases with electrode thickness, compared with conventional planar electrodes prepared by stacking dense layers of active materials on current collector films. The decreased efficiency of charge transfer and mass transfer because of inefficient electrical conduction, impeded ion diffusion, and reduced reaction site accessibility can cause inhomogeneous distributions of electric potential, ion concentration, and electrochemical reaction across the electrode. Thus, during charge/discharge, longer time, more electrons/ions, and a higher overpotential are required to fully utilize all active materials in the interior of electrodes, which can degrade the rate capability and undermine the increased energy density. Here, we identify some critical breakthroughs and strategies that will aid in further improving the performance of EESDs by overcoming the transport limitations. These include promising additive manufacturing techniques, methods to integrate an energy-dense active material into the electrode, the development of 3D-printable inks and resins, and the use of design optimization to predict the optimal architecture of an electrode for a given objective and constraint.