Ultrasmall SnO2 nanocrystals sandwiched into polypyrrole and Ti3C2Tx MXene for highly effective sodium storage

Abstract

The main challenge for developing transition metal oxides (TMOs) as anode materials for sodium-ion batteries (SIBs) is to rationally design and synthesize TMO-based hybrid structures and precisely control the transport of ions and electrons. Herein, we propose a facile in situ interfacial growth strategy to achieve a novel sandwich structured P-SnO₂/Ti₃C₂ composite, where SnO₂ nanocrystals modified with an ulthathin polypyrrole (PPy) layer of about 3 nm are strongly coupled with Ti₃C₂T_x Mxene nanosheets through Sn–O–Ti chemical bonds. Uniformly dispersed SnO₂ nanocrystals confined in PPy and Ti₃C₂T_x nanosheets provide abundant acitve sites, while the conductive polymer PPy and Ti₃C₂T_x serve as robust protective layers alleviating the volume expansion and fast channels for Na ions and electron transport. Thanks to the advantages of structure and composition, the resulting P-SnO₂/Ti₃C₂ anode demonstrates excellent sodium storage properties in terms of long cycle life (325.6 mA h g⁻¹ at 100 mA g⁻¹ after 100 cycles) and outstanding rate performance (204.4 mA h g⁻¹ at 1000 mA g⁻¹). The density functional theory calculations further prove that the P-SnO₂/Ti₃C₂ heterostructure can balance the adsorption and release of Na atoms on the interface, thus boosting the performance of SIBs. This approach developed can also provide valuable guidance for the constuction of more functional TMO-based composites.