3D Architected Pyrolytic Carbon Electrodes with Multi-Scale Controlling Factors

Abstract

Engineering electrode architecture in rechargeable batteries has the potential to control transport trajectories of ions and electrons, which can significantly affect battery performance especially at high current rates and at high mass loadings. Many efforts have been dedicated to develop novel methods of engineering electrode architecture that include extrusion-based additive manufacturing and using sacrificial templates. These methods are limited in terms of producing resilient structures that can withstand the mechanical loads imposed during operation of the cell and are not yet capable of producing geometries that enable independent control of form factors in multi-scale ranges from micron to centimeters scales. We developed a facile fabrication method of 3D architected carbon anodes using direct light processing (DLP) 3D printing of UV-curable resin and subsequent pyrolysis in an inert atmosphere. The specific architecture of these electrodes is fully controllable over every length scale: from local geometry (micrometer-scale) to control tortuosity and mass loading, as well as global geometry (centimeter-scale), to intergrade into any device geometries. In addition, the architected pyrolytic carbon electrode is free-standing and binder-free, enabled by the monolithic structure and great electrical conductivity of carbon. To demonstrate the architected carbon electrode as an anode in lithium ion batteries, we fabricated 1 mm-thick 3D periodically architected carbon electrodes with simple cubic-like geometry and characterized its electrochemical performance by constructing a half-cell against a lithium metal counter electrode. Battery cycling of these electrodes using a coin cell showed reversible capacity of ~230 mAh/g (or 7 mAh/cm2) at a 16 mA/g (or 0.6 mA/cm2) and its capacity retained over 85 % until 100 cycles. Uniaxial compression tests revealed its high structural integrity, enabling the architecture to be maintained even after 300 cycles under pressure in a coin cell. We further studied a correlation between electrode architecture design and battery performance by varying transport path of Li-ion in electrolyte independently from tortuosity of porous structure and Li-ion transport path in the electrode. In addition, key considerations to optimize electrode architecture will be discussed based on the comparison between stochastic structure of conventional slurry and designed electrode architecture under the same electrode material. This multi-scale tunable fabrication method may give a new path not only to electrode design in conventional planner cells but also to a 3D interdigitated full battery.