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

Abstract

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 °C in flowing O₂(g) or Ar(g). The highly disordered structure of as-prepared cryo-RuO₂ is transformed to rutile RuO₂ at 200 °C in O₂(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 °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 °C. This study provides processing guidelines to achieve fabrication of 3-D microbattery architectures containing a nanoscopic RuO₂ electrode component.