Tuesday, 11 October 2022
Designing a solid-state battery is a balancing act. Fast charging rates and high capacity are preferable, but safety and long battery lifetimes must also be preserved. When making a solid-state electrolyte, amorphous materials with greater lithium content are ideal—they have greater conductivity than their lower-lithium-content counterparts. In addition to high lithium content, recent studies have focused on eliminating grain boundaries in solid state electrolytes. Eliminating grain boundaries allows for safer charging and discharging by reducing the chances of dendrite formation and subsequent shorting. Through experiments, we tried to reconcile amorphous character and relatively higher lithium content to produce a mechanically robust, conductive electrolyte material that lasts over many cycles. We first coarsened Li3BO3 powder in a tube furnace, then pelletized the powder at 253,411 bar via hydraulic press. The rapid joule heating method involves two carbon papers connected in parallel with a DC power supply. Using this configuration, we had access to rapid quenching rates that typically require expensive technology. Resistance from the carbon paper resulted in a rapid temperature increase proportional to the applied current so the carbon paper acted as a heating element. The Li3BO3 pellet was inserted between the two papers where it heated to its melting temperature (760-880°C) within 20 sec. We hypothesized that shorter ramping and cooling times introduced by rapid joule heating would promote amorphous character in Li3BO3, compared to samples prepared in a tube furnace with longer heating and cooling times. Full width at half maximum values calculated from X-ray diffraction results for each sample suggest the samples prepared using rapid joule heating formed smaller crystalline domains than those manufactured in the tube furnace. Scanning electron microscopy images taken at 5.0k magnification confirm this calculation. Large grains can be seen in the traditionally heated sample whereas no grains are observable in the rapid joule heated sample. Smaller crystalline domains emphasize the effects of rapid cooling and encourage future studies in escalating heating and cooling rates to produce amorphous or partially amorphous electrolytes.