The importance of combining disorder with order for Li-ion insertion into cryogenically prepared nanoscopic ruthenia

Cryogenically prepared RuO2 ( cryo-RuO2), a material known for its ability to self-wire'' into continuous, nanoscopic electronic pathways, is proposed as an electrode for Li-ion microbatteries with three-dimensionally interpenetrated components. We determined processing guidelines that optimize Li-ion uptake in cryo-RuO2 powders by varying the solid-state structure of cryo-RuO2 with thermal processing at 50-250 degrees C in flowing O-2( g) or Ar( g). The highly disordered structure of as-prepared cryo-RuO2 is transformed to rutile RuO2 at 200 degrees C in O-2( g), resulting in a 60% loss of Li-ion capacity ( as-prepared: 214 mA h g(-1); rutile: 84 mA h g(-1)). In contrast, thermal processing in Ar( g) preserves structural disorder in the cryo-RuO2, even up to 250 degrees C. The highest Li-ion capacity occurs for the treatment that mixes order ( crystallinity) with disorder: >250 mA h g(-1) for cryo-RuO2 heated in oxygen to 50 degrees C. This study provides processing guidelines to achieve fabrication of 3-D microbattery architectures containing a nanoscopic RuO2 electrode component.