Competition between dissolution and ion exchange during low temperature synthesis of LiCoO2 on porous carbon scaffolds†

The intentional design of ionic and electronic pathways in battery electrode architectures is one strategy to optimize battery performance and maximize the utilization of expensive and/or scarce electrode active materials. Porous carbon scaffolds are particularly attractive for advanced electrode architectures due to their light weight and low cost. One major challenge for insertion-type Li-ion battery electrodes utilizing porous carbon scaffolds is direct electrical wiring of commercially relevant electrode materials. In particular, lithium metal oxide cathode materials require high synthesis temperatures (>700 °C in air) that exceed the stability of carbon (∼450 °C). In this work, we studied the mechanism of LiCoO₂ deposition onto porous carbon scaffolds from a low temperature (<300 °C) process involving electrodeposition, hydrothermal synthesis, and heat treatment (<300 °C). We determined how variables during hydrothermal synthesis, such as pressure, temperature, duration, and LiOH concentration, influence the synthesis mechanism and resulting LCO crystal structure and microstructure. We found that low hydrothermal pressure and high LiOH concentration favor an ion-exchange mechanism and the formation of nanoflake LiCoO₂, while high hydrothermal pressure and low LiOH concentration led to a dissolution–precipitation mechanism and nanoscale LiCoO₂. We further demonstrated the versatility of the ion exchange mechanism to deposit LiCoO₂ on a variety of monolithic porous carbon scaffolds. Overall, this research provides insight into the versatility, and limitations, of soft chemistry strategies to deposit commercially relevant Li-ion oxide cathode materials directly onto unique porous carbon scaffolds.