A strategy to fabricate flexible freestanding sandwich-like film based on sulfur heterocyclic quinone polymer for flexible solid-state Zn-ion battery

A challenge faced by quinone polymers for application in flexible solid-state Zn-ion batteries (FSZIBs) is how to design and fabricate their flexible free-standing electrodes with high capacity and excellent cycling stability. Here, a two-step engineering strategy including fabrication of polymer nanowire and construction of sandwich-structured film was developed to achieve a flexible freestanding film based on sulfur heterocyclic quinone polymer (SHQP) for FSZIBs. A core/sheath structured carbon nanotube@SHQP(CNT@SHQP) nanowire was first synthesized by the interfacial polymerization method, in which the π-π interaction between SHQP and CNT promoted the self-assembly of SHQP to form thin nanolayers around CNT. This unique nanostructure was effective in increasing active sites, accelerating electron transfer, shortening the diffusion path of Zn²⁺ ions, buffering the volume variation while simultaneously enhancing the structural stability of SHQP nanolayers. More importantly, a sandwich-like hierarchical film of reduced graphene oxide|CNT@SHQP|reduced graphene oxide (rGO|CNT@SHQP|rGO) was designed and fabricated using CNT@SHQP nanowires and GO nanosheets through vacuum filtration and further mild reduction. The flexible Zn//rGO|CNT@SHQP|rGO battery exhibited a high capacity (139.9 mA h g⁻¹ at 0.1 A g⁻¹) and long-term cycling stability (76.2 % of the initial capacity after 2000 cycles at 1 A g⁻¹). This strategy can be further extended for fabricating flexible free-standing films of other quinone polymers, which have great potential application in wearable electronics.