An ultralight and flexible sodium titanate nanowire aerogel with superior sodium storage

Abstract

An ultralight, conductive, and flexible 3D assembly of a metal oxide nanowire aerogel as an electrode for energy storage devices without additives and typically inconvenient flexible supported-substrates remains a challenge. Herein, we report a new 3D highly ordered layer-by-layer stacking sodium titanate@reduced graphene oxide core–shell (NTO@GCS) nanowire aerogel that has an ultra-high aspect ratio with a diameter of 30–50 nm and typical length up to 100 μm for a new class of convenient sodium-ion battery (SIB) anodes. The formation mechanism of the unique 3D NTO nanowire aerogel, the precursor of the NTO@GCS aerogel, was carefully proposed, demonstrating that the key challenge for this synthesis strategy was to form a stable and homogeneous ultrafine NTO nanotube gel suspension. In addition, for high performance sodium-ion storage, reduced graphene oxides (rGOs) were introduced into the NTO aerogel backbone. The critical role of the graphene structure between the NTO nanowires and rGO sheets in Na⁺ storage was systematically investigated. Compared to the 3D pristine NTO aerogel and 3D NTO nanowires on graphene sheet paper, the 3D interconnected NTO–GCS aerogel electrode facilitated rapid ion/electrolyte transportation, resulting in remarkably enhanced Na⁺ storage with a reversible capacity of 240 mA h g⁻¹ at 0.2C and durable cycling stability after 4900 cycles at a rate of 2 and 4C with nearly 100% coulombic efficiency.