Competition between dissolution vs. ion exchange during low temperature synthesis of LiCoO2 on carbon scaffolds

Deterministic design of electrodes is the concept of intentionally designing and controlling the electrode architecture to achieve high capacity and rate capability, leading to high power and high energy devices. Utilizing 3D conductive scaffolds for deterministic electrode design could unlock new applications for energy storage devices in structural energy storage and wearable electronics. One challenge is to obtain direct wiring of commercially-relevant electrode materials to 3D scaffolds such as porous carbon materials. For example, the synthesis of lithium metal oxide cathode materials requires high temperatures (>700°C) that exceed the stability of conductive carbon-based scaffolds (~400°C). In this work, we studied the aqueous chemistry of Co(OH)2 to build a mechanistic understanding of a combined electrodeposition-hydrothermal synthesis along with mild heat treatment (<300°C) to obtain crystalline, layered LCO on 3D carbon scaffolds using only 3 feedstock materials. We established an understanding of how hydrothermal treatment pressure, temperature, duration, and LiOH concentration modulate the active synthesis mechanism and resulting LCO morphology. We find that in particular low hydrothermal pressure and high LiOH concentration prevent dissolution of precursor Co(OH)2 to enable an ion-exchange of H+ from Co(OH)2 with Li+ from solution to produce layered LCO while preserving the nanoflake architecture on the scaffold. We demonstrated the versatility of the ion-exchange process to coat a variety of electrode geometries and architectures. Overall, this research provides insight into the versatility, and limitations, of soft chemistry strategies to crystallize commercially relevant Li-ion cathode materials directly onto unique geometries for wide-ranging applications.