Polyol-mediated carbon-coated Li₄Ti₅O₁₂ nanoparticle/graphene composites with long-term cycling stability for lithium and sodium ion storages

Nano-sized oxides are investigated to improve rate capability by decreasing ion and electron travel length. However, extended contact area of nano-sized oxides with electrolyte causes undesirable side reactions and poor cycling stability. Interestingly, previous studies focus either on preparation of nano-sized oxides or on carbon coating to prevent side reactions. In this study, a microspherical composite of ethylene glycol-derived in situ carbon-coated Li₄Ti₅O₁₂ nanoparticles and reduced graphene oxide is prepared by polyol-mediated spray drying method using ethylene glycol as a stabilizer to control particle growth and ethylene glycol coordinated with Ti precursor as a carbon source. The composite shows excellent rate capability as anode materials for lithium-ion and sodium-ion batteries. Most importantly, the composite shows 94% capacity retention after 3000 cycles at 10 C for Li⁺ storage and 95% capacity retention after 1000 cycles at 5 C for Na⁺ storage at room temperature. At 60 °C, furthermore, composite shows 93% capacity retention after 1000 cycles for Li⁺ storage and 95% capacity retention after 500 cycles for Na⁺ storage at 10 C. The post-mortem analysis confirms that in situ carbon coating on Li₄Ti₅O₁₂ effectively prevents direct contact of Li₄Ti₅O₁₂ nanoparticles with electrolyte, thus, blocking side reactions and greatly improving cycling stability.